In no way are my comments intended to dismiss the very real and growing threat of Islamist terrorism in the U.K.; however, I find the "conservative" estimate of 200 suicide bombers in the U.K. to be a bit of a reach.

While a lot of young and not so young want to be jihadists will brag about their desire to die as a martyr for the cause, most suicide bombers (the real ones) undergo an intensive indoctrination period (or brainwashing) and then held in isolation until it is time to hit the target, because historically it has been demonstrated that they'll have a change of heart if they're allowed to rejoin society and become a sleeper bomber of sorts. Maybe there are Islamist safe havens within the U.K. where 10s of would be suicide bombers are isolated from the rest of society, but it seems unlikely. Of course I need to caveat the above statement that not all suicide bombers require extensive indoctrination (they're already true believers) and can hide in society openly for months and still hit their target as many of the 9/11 attackers did.

One report quoted an MI6 officer's briefing to US officials in which he said: "The internal threat is growing more dangerous because some extremists are conducting non-lethal training without ever leaving the country. Should these extremists then decide to become suicide operatives, HMG [Her Majesty's Government] intelligence resources, eavesdropping and surveillance would be hard pressed to find them on any 'radar screen'."
What type of non-lethal training are they talking about? Indoctrination?

There is no doubt that the insider threat is a growing concern in Europe and possibly the U.S. (especially the lone wolf attacks), but a suicide attack is an entirely different level. If they have the infrastructure in place within Europe (and in this case the UK) to indoctrinate, radicalize, inspire tens of individuals to conduct a suicide attack, and then of course actually provide the materials to do so (a topic not addressed in the article) then the threat is worse than I thought.