Compromising an ongoing investigation

Tonight's midnight news on BBC Radio 4 cited an unnamed "Capitol Hill source" for the claim that there are still 5 liquid bomb plotters at large, who may have activated a Plan B. Since Republican House member Peter King was using exactly the same language today on US news programs, King is almost certainly the source for the BBC claim as well. Clearly the BBC could not find any British source willing to go on record about the claim, which suggests that King has revealed information that the police and MI5 did not want exposed. This is the same Peter King who was calling for prosecutions of newspapers for disclosing details of anti-terrorism investigation a few weeks ago.