Speaking on LBC Radio, Mr Johnson was asked whether he feared retribution attacks after calling Jihadists “porn-driven losers” and “literally w******”.
He replied “of course not”, and continued: “At any one time, there are a large number of people – perhaps in the low thousands – who do present some measure of potential risk.”
Asked how many, the London Mayor added: “In the low thousands ... Maybe three, four [thousand], something like that. These are ballpark figures. “
Mr Johnson added that the statistics were “well in the public domain” but repeatedly refused to say if they came from discussions with the Metropolitan Police or MI5.
Last week, Mr Johnson claimed young British jihadists are pornography-obsessed inadequates who only turn to radical Islam when they fail to “make it with girls”.
Speaking on a visit to Kurdistan, he called for the terrorist group to be “demystified”, and its feared recruits unmasked as “tortured losers”.
He told the Sun: “If you look at all the psychological profiling about bombers, they typically will look at porn. They are literally w******. Severe onanists."