According to British Intellegence.
This is an odd move. Can't help but think he's been told to do this to push the American Public to accept military strikes on Iran. I mean hell, he's even gone so far as to mention how MI6 foiled their attempts numerous times as early as 2008. How often does an intellegence agency admit that completely unprovoked? Argueably you could take it as a claim of responsibility for all those killed scientists.
Can't help but wonder if this is shades of FDR, and Obama is trying to push that info out there through MI6 due to Bush's discrediting of the CIA due to that other WMD announcement.
Either that or MI6 is 100% positive of this and is just worried the US won't act.