Coalition press conference - trouble at t'Home Office?

Once each minister (Nick Clegg, Theresa May, Vince Cable, George Osborne, David Cameron) had delivered their set-pieces, the prime minister took questions from the press pack.

As part of Cameron's inclusive style of government, he farmed out the task of answering to his ministers - both Tory and Lib Dem - when the questions touched on their areas of departmental responsibility.

With one exception: Theresa May. There was an immigration question - clear Home Office territory - but Cameron fielded it himself and didn't invite May to comment.

Possible reasons?

1. Cameron and May are so close that he knows he can speak for her.
   OR
2. Cameron and May are not close enough and he doesn't trust her to speak for him.
   OR
3. Immigration policy is still too woolly to be given a straight answer (still no real clarity on how the immigration "cap" is to be set), so Cameron preferred to dead-bat the question and move on.