Cameron and Clegg try to put Coalition back on track

The strains in the Coalition have never been greater but today the two men who have largely held it together - David Cameron and Nick Clegg - will try to put it back on track once again.

They're launching a major programme of railway investment. But as usual at these events, it will be less what they say than how they say it which matters.

Will there be any hint of a new type of partnership - one where the men emphasise their differences rather more, the views they share in common rather less?

Certainly some Tory backbenchers are calling for a greater differentiation between the parties.

The former Defence Secretary recently pointed out that, in terms of seats, the Liberal Democrats are "a sixth of the Coalition, not half the Coalition".

David Cameron told the Sunday Times that there were "profound areas of disagreement" between the two parties. But he also said it was important not to tolerate what he called "naval-gazing".

The railway investment plan will be an ideal opportunity for the Prime Minister and his deputy to show this is a Coalition held together by economic necessity. A nuts-and-bolts alliance with a real purpose now - but not built to last forever.