Top 13 IT security consulting firms based in London, United Kingdom

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 IT security consulting firms, so some rows will be adjacent to the category rather than pure plays. The description and evidence 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 SmartSearch, 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 “IT security consulting firms”. Matching reads each company's description, not its industry code or its name.

What we exclude

Companies whose own description does not clearly place them among IT security consulting firms, 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 an evidence 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, 2,048 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 4, 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.