Maggie and the 'special relationship'.

Cameron is attempting to be the first Tory leader to fully distance himself from Thatcher and move the Party away from her influence. This has included criticism of globalisation and America's role in the world as well as apologising for the Thatcher era Tories calling Mandela a terrorist. Of course many Tories are unhappy about this and some still look back with nostalgia for the Thatcher era.

Cameron must have felt he was safe from Thatcher's meddling and attempts to grab back some influence. Doctors had ordered her not to talk in public due to poor health. But somehow she has emerged to re assert her views and special relationship with the US. For dramatic effect this has been on the same day Cameron gave a speech tinged with some criticism of US foreign policy .
Thatcher chose her moment well, the 5th anniversary of 9/11.

Blair has made no secret of his admiration for Thatcher but he has not learnt the lesson from her departure, knowing when to go. Perhaps he will emulate her in the future, always trying to grab back centre stage and undermine his successors, never accepting he is no longer wanted.
Blair has started this process already with the undermining of the frontrunner to succeed him, Brown.