Company lists · Data refreshed September 2026
Top 25 Outsourced sales call centers based in London, United Kingdom
RevenueBase identified 125 outsourced sales call centers headquartered in London, United Kingdom as of September 2026 and tracks 1,739 professional contacts across them, including 138 with verified work emails. Across the United Kingdom, London is the largest hub for this category.
This list covers outsourced sales call centers headquartered in London, United Kingdom, matched on what each company actually does as described in its own words. Ranked by team size, largest first. Every row shows the company's own description, its RevenueBase Smart Search rating, and when it was last checked. Data refreshed September 29, 2026.
Published by RevenueBase, a B2B data infrastructure company. This list was built with RevenueBase Smart Search, the natural-language company search RevenueBase customers use to build their own targeted lists and unlock verified emails and direct dials at the companies on them. How these lists are built and judged.
The 25 largest outsourced sales call centers based in London, United Kingdom
Ranked by team size| # | Company | Contacts | |||
|---|---|---|---|---|---|
| 1 | 569 contacts → | ||||
Partial evidence “Vertex is a leader in BPO and Customer Management Outsourcing, serving over 200 clients worldwide across many sectors.” Source: RevenueBase Database · checked Sep 29, 2026Thanks. The Data Team will review it. | |||||
| 2 | 98 contacts → | ||||
Indirect evidence “Founded in 1988, RSVP is the oldest provider of contact centre services in the UK.” Source: RevenueBase Database · checked Sep 29, 2026Thanks. The Data Team will review it. | |||||
| 3 | 90 contacts → | ||||
Partial evidence “A world class offshore outsourcing agency, with offices in London and Harare, we have access to some of the best educated, best spoken graduates you will find anywhere in the…” Source: RevenueBase Database · checked Sep 29, 2026Thanks. The Data Team will review it. | |||||
| 4 | 62 contacts → | ||||
Partial evidence “Support Adventure is an outsourcing company that specializes in customer service and support.” Source: RevenueBase Database · checked Sep 29, 2026Thanks. The Data Team will review it. | |||||
| 5 | 59 contacts → | ||||
Partial evidence “CallCare is your outsourced contact centre and customer service partner.” Source: RevenueBase Database · checked Sep 29, 2026Thanks. The Data Team will review it. | |||||
| 6 | 59 contacts → | ||||
Partial evidence “Looking to fill your calendar with qualified calls?” Source: RevenueBase Database · checked Sep 29, 2026Thanks. The Data Team will review it. | |||||
| 7 | 48 contacts → | ||||
Strong evidence “At Fly Pie, sales outsourcing isn’t a “done-for-you” service, it’s a growth engine we build with you.” Source: RevenueBase Database · checked Sep 29, 2026Thanks. The Data Team will review it. | |||||
| 8 | 46 contacts → | ||||
Partial evidence “Direct Response can provide outsourcing of voice, data and contact centre services for organisation from a global business to a one-man operation, delivering outstanding service…” Source: RevenueBase Database · checked Sep 29, 2026Thanks. The Data Team will review it. | |||||
| 9 | 40 contacts → | ||||
Indirect evidence “Kingdom Vision is a medium to take your business from good to great.” Source: RevenueBase Database · checked Sep 29, 2026Thanks. The Data Team will review it. | |||||
| 10 | 16 contacts → | ||||
Strong evidence “Kimon Services provides high-quality outsourced staff across various industries and disciplines, including customer service, data entry, call centres, marketing and sales support…” Source: RevenueBase Database · checked Sep 29, 2026Thanks. The Data Team will review it. | |||||
| 11 | 16 contacts → | ||||
Indirect evidence “Big Wolf Marketing - Leaders in B2B Telemarketing, Lead Generation & Appointment Setting With a vast combined experience, implementing established and cutting edge innovative…” Source: RevenueBase Database · checked Sep 29, 2026Thanks. The Data Team will review it. | |||||
| 12 | 14 contacts → | ||||
Strong evidence “We are an outsourcing agency specializing in sales, marketing, and customer support.” Source: RevenueBase Database · checked Sep 29, 2026Thanks. The Data Team will review it. | |||||
| 13 | 11 contacts → | ||||
Partial evidence “We increase sales leads by 50% and achieve 99% customer satisfaction with our UK- and US-based team.” Source: RevenueBase Database · checked Sep 29, 2026Thanks. The Data Team will review it. | |||||
| 14 | 10 contacts → | ||||
Strong evidence “Transaction Focus is a leading Global outsourced sales and marketing company with headquarters in the United Kingdom with connections and associates based in China,the USA…” Source: RevenueBase Database · checked Sep 29, 2026Thanks. The Data Team will review it. | |||||
| 15 | 8 contacts → | ||||
Strong evidence “Confero is a UK based outsourced call centre business, focussed on delivering high quality inbound, outbound, and digital services to our clients.” Source: RevenueBase Database · checked Sep 29, 2026Thanks. The Data Team will review it. | |||||
| 16 | 8 contacts → | ||||
Indirect evidence “Experts in having great conversations, REAL Calling are part of the REAL Family that has been delivering industry-leading face to face fundraising for over 13 years in the UK.” Source: RevenueBase Database · checked Sep 29, 2026Thanks. The Data Team will review it. | |||||
| 17 | 8 contacts → | ||||
Indirect evidence “Founded in May 2007, O.B.S.” Source: RevenueBase Database · checked Sep 29, 2026Thanks. The Data Team will review it. | |||||
| 18 | 7 contacts → | ||||
Partial evidence “At alaouico, we understand the challenges businesses face with customer interactions-whether it's managing high call volumes, ensuring timely responses, or maintaining customer…” Source: RevenueBase Database · checked Sep 29, 2026Thanks. The Data Team will review it. | |||||
| 19 | 3 contacts → | ||||
Partial evidence “As experts in harnessing technology to enhance vital stages of the sales journey, we empower you to delegate tasks such as lead acquisition, nurturing, follow-ups, and data…” Source: RevenueBase Database · checked Sep 29, 2026Thanks. The Data Team will review it. | |||||
| 20 | 2 contacts → | ||||
Indirect evidence “BringCommerce | Outbound Lead Gen That Actually Works We help B2B service businesses flood their pipeline with qualified leads by fixing positioning, power messaging and outbound…” Source: RevenueBase Database · checked Sep 29, 2026Thanks. The Data Team will review it. | |||||
| 21 | 2 contacts → | ||||
Partial evidence “At Niche, it is not about the number of calls made but about quality.” Source: RevenueBase Database · checked Sep 29, 2026Thanks. The Data Team will review it. | |||||
| 22 | 1 contacts → | ||||
Partial evidence “Nsibandze Outsourcing (“NOS”) is a global CX business on a mission to ignite opportunity for small and medium sized companies through telemarketing, lead generation, data analysis…” Source: RevenueBase Database · checked Sep 29, 2026Thanks. The Data Team will review it. | |||||
| 23 | 1 contacts → | ||||
Indirect evidence “Specialists in client acquisition, we help B2B businesses sign 2-3 high ticket clients in 35 days or less.” Source: RevenueBase Database · checked Sep 29, 2026Thanks. The Data Team will review it. | |||||
| 24 | 1 contacts → | ||||
Indirect evidence “Grow your business through Lead generation and customer relationship management of new or your existing client base.” Source: RevenueBase Database · checked Sep 29, 2026Thanks. The Data Team will review it. | |||||
| 25 | 1 contacts → | ||||
Indirect evidence “Uniconnect One offers tailor-cut solutions to business owners who are trying to upscale their businesses.” Source: RevenueBase Database · checked Sep 29, 2026Thanks. The Data Team will review it. | |||||
RevenueBase Smart Search
RevenueBase Smart Search assesses information from a company’s LinkedIn profile, information supplied directly by the company, its website, and other publicly available sources. It uses that information to rate how closely the company relates to this list’s category: outsourced sales call centers. Every row carries its rating and the description the rating was read from, so each one can be checked rather than taken on trust.
- Strong evidence
- The company's own public description of its business names outsourced sales call centers.
- Partial evidence
- Its own public description names part of outsourced sales call centers, so it works in or next to the category without describing itself that way.
- Indirect evidence
- The description shown does not name outsourced sales call centers. The match rests on the rest of the company's public profile rather than the one sentence quoted here, so this is the rating to check first.
RevenueBase Smart Search is how these lists are built: RevenueBase's data engine and AI assemble the companies that match a category defined in a user's own words, so a list can be about what companies actually do rather than about whichever industry code they were filed under.
Showing 25 of 125 outsourced sales call centers based in London, United Kingdom
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Outsourced sales call centers based in London, United Kingdom at a glance
As of Sep 29, 2026Companies by employee count
Email recency for this list is measured across the whole United Kingdom list rather than for London, so it is reported there. Company counts and contact totals on this page are exact for London, over 125 companies.
How this list was built
Company categories are rarely black and white. RevenueBase reads each company's own description of its business to decide whether it belongs among outsourced sales call centers, so some rows will be adjacent to the category rather than pure plays. The description and RevenueBase Smart Search rating on every row are there so you can check each match yourself.
- Source
- The RevenueBase company graph: 60 million companies and 398.9 million professional contacts resolved from primary sources, queried with RevenueBase Smart Search, the natural-language company search available to every RevenueBase user.
- What qualifies
- Companies headquartered in London, United Kingdom whose own description of what they do matches “outsourced sales call centers”. Matching reads each company's description, not its industry code or its name.
- RevenueBase Smart Search
- RevenueBase Smart Search is how this list is assembled and how each row is rated. RevenueBase's data engine and AI assess a company's LinkedIn profile, information supplied directly by the company, its website and other publicly available information, then relate it to a category defined in a user's own words. Each row is rated strong evidence (its own description names outsourced sales call centers), partial evidence (it names part of the category) or indirect evidence (the description shown names none of it and the match rests on the rest of the company's profile). The description supporting each rating is quoted on the row.
- What we exclude
- Companies whose own description does not clearly place them among outsourced sales call centers, and records with no verified work email. Companies headquartered outside London are excluded even when they keep an office there.
- Match quality
- In blind human judging of this matching method, 86% of matched companies were on target. Expect roughly 1 in 7 rows to be adjacent to the category rather than a pure play. Every row shows the company's own description and its RevenueBase Smart Search rating so you can judge each match yourself. Read the full methodology: how the lists are built, how the judging worked, and what the figure means.
- Ranking
- Team size, largest first: companies are ordered by the number of professionals RevenueBase tracks at each one. Employee ranges shown are reported bands, for context.
- Verification
- Every listed company carries at least one verified work email, 138 across the full list. Contacts re-verify on a rolling cadence, and each contact's own verification date is shown inside RevenueBase.
- Refresh
- This page's figures were pulled from the company graph on September 29, 2026. Lists refresh periodically as the graph is re-checked.
- Corrections
- Wrong category, wrong headquarters, or a company that has closed? Use “Report an issue” on any row. Reports go to the RevenueBase Data Team and feed back into the company graph.
Frequently asked
What is RevenueBase Smart Search?
RevenueBase Smart Search is how RevenueBase decides which companies belong on this list and how strongly each one fits. Its data engine and AI assess a company's LinkedIn profile, information supplied directly by the company, its website and other publicly available information, then relate it to the category the list is about. Each row is rated strong evidence when the company's own description names outsourced sales call centers, partial evidence when it names part of the category, and indirect evidence when the description shown names none of it and the match rests on the rest of the company's profile.
How many outsourced sales call centers are there based in London, United Kingdom?
RevenueBase identified 125 outsourced sales call centers headquartered in London, United Kingdom as of September 2026, matched on each company's own description of what it does rather than its industry code.
What is the largest company on this list?
Vertex Data Science, headquartered in London, tops this list with the largest team on record.
Which city in the United Kingdom has the most outsourced sales call centers?
London leads the United Kingdom with 125 headquartered companies, followed by Manchester (19) and Birmingham (11).
How do I get contact information for these companies?
A free RevenueBase account lets you run this exact search and work the top results, verified emails and direct dials included. Upgrading unlocks all 138 verified decision-maker contacts tracked across these 125 companies.
How current is this list?
The list refreshes periodically as the company graph is re-checked. This page's figures were pulled on September 29, 2026.
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About this data
RevenueBase is a B2B data infrastructure company. Its company graph covers 60 million companies and 398.9 million professional contacts, with emails verified on a rolling cadence rather than scraped once and left to decay. These company lists are generated directly from that graph with RevenueBase Smart Search, the same natural-language company search every RevenueBase user has: describe a market in plain words, get the companies that match, and add verified emails and direct dials for the people at them. It is the same data that powers RevenueBase's B2B data products, and a free account includes 500 credits to start. How these lists are built and judged.
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