The leaked WikiLeaks documents, written by senior US military commanders at Guantánamo Bay, illustrate how, for two decades, Britain effectively became a crucible of terrorism, with dozens of extremists, home-grown and from abroad, radicalised here.

Finsbury Park mosque, in north London, is described as a “haven” for extremists. United States intelligence officials concluded the mosque served as “an attack planning and propaganda production base”.

The files will raise questions over why the Government and security services failed to take action sooner to tackle the capital’s reputation as a staging post for terrorism, which became so established that the city was termed “Londonistan”.