How many?

@DannyShawBBC Tweeted thusly:
'Security Minister Ben Wallace tells BBC the pool of 'former subjects of interest' is between 12,000-18,000. Abedi was in that pool.   12:13 PM - 26 May 2017'

12,000 to 18,000 potential Islamist terrorists in the UK? That seems rather worrying to me but I'm sure that the BBC will point out that the real fear is an Islamophobic backlash.