Ex-MI5 officer David Shayler alleged so at a public meeting in Bristol last week, as was reported in the Bristol Evening Post. Money quote:

Unfortunately, Shayler's exact words were not reported, making it difficult to assess the claim. Luckily, I found a recording of his words at this website.

Shayler was speaking to 9/11 sceptics in Bristol. They showed a video, then he spoke and took questions. The topic moved from 9/11 to the July 7th bombings in London. Shayler suspects the British security services might have had a hand in 7/7. An audience member asked about MI5's possible complicity in 7/7, and, if so, whether Tony Blair's government was involved or were kept in the dark. This was Shayler's response [my transcription]:

Yeah, I mean, I don't know how involved Blair is - it's a difficult question to answer. I mean, certainly I know, as I say, the intelligence services do things behind the backs of government, the cabinet and parliament - it's very easy in this country to do that, as there's no oversight of the services. And, in some ways, they don't want the government to know, so, when they are sent out to deny these things, as Robin Cook was, they can do it looking honest, basically.

But I think the only way we can explain Blair's behaviour is that he is blackmailable by the intelligence services. I know that the intelligence services have files on most of the Labour government because I saw some of the files while I was there. In fact ... [inaudible audience interjections, laughter] ...Well, one of the things I want to tell you is that - I actually, I didn't see this myself, I must admit - but somebody who was reviewing Blair's file, this was when Blair was unknown really, in 1992, not particularly well known, told me that Blair was an MI5 agent. In the 1980s he'd reported on members of CND and the so-called Trotskyists in the Labour Party. Now, I've tried to get to the bottom of this, it's very difficult. But it would in some way explain why he does what he does, basically, because he's actually a stooge, he's one of them, basically.

Shayler may be wrong about many things, but he's right that the Blair-as-MI5-agent report has much explanatory value. But whether Blair needed to be blackmailed to act for MI5 is another matter - Blair's naivity, vanity and ambition, coupled with the state of the Labour Party in the 80s - may have been sufficient motivation for him to inform on "left-wing extremists" to his MI5 contacts. (But then that act of informing might itself become a blackmailable vulnerability, so perhaps Shayler's right after all.)

I dread to think what might be in Gordon Brown's file.