The serious suspects were the ones singled our as those "thought to be a serious threat to Britain's security" - as described in the MI5 report.
Yes. That is them.
People like at least one of the suspects, who had attempted to reach Somalia to train with Al Shabab.
He was on that list with "thousands" more.

Now you are claiming there are what? - 2000, wasn't it?
I am saying 2000 at the very least, and for all the reasons and facts given.
You believe it is substantially less, but you have never told us what reason you have for that belief.
Will you list your reasons for us now Jim dear?