Almost 700 terror investigations are being carried out by the security services.
The figures were revealed yesterday after a car ploughed into cyclists outside Parliament in an apparent extremist attack.
Britain was on a heightened state of alert last night, with Theresa May warning that the threat was now ‘one of the starkest we have faced’.
Security minister Ben Wallace said the increased danger of attacks was ‘here to stay’. Their warnings came as anti-terror police tried to question a suspect over the latest feared targeting of Westminster.