What did America know about Britain's Al Qaeda spy?

Aimen Dean is a founder member of al-Qaeda, who changed tack in 1998 and became a spy for Britain's security and intelligence services, MI5 and MI6. Interviewed by Peter Marshall, he describes his years working in Afghanistan and London as one of the West's most valuable assets in the fight against militant Islam.

Listen on to hear Michael Scheuer, the former CIA man hunting for Bind Laden, who says he wish he knew about Dean sooner.