Migrant crisis: Cameron's 'head and heart' strategy

Expect the prime minister to use Downing Street's phrase of the moment "head and heart" when he gets to his feet in the Commons later.

That's Number 10's chosen way of explaining why he has completely changed his position on allowing more refugees in, while still trying to hold on to their main argument - not easy.

The immediate question, and Westminster guessing game, as MPs return from their summer break is how many more Syrian refugees the UK will accept, directly from the borders of that war torn country.

Mr Cameron has shifted his position dramatically in the past seven days, and is expected to say that over 10,000 of the most vulnerable will be brought to the country.

But while it's seemed, politically, he had no choice but to do something of that scale in the face of the public's response in the last few days, the government is all too aware it is trapped in a conundrum.

Ministers are loathe to do anything that makes the UK appear a more attractive destination for migrants - one said to me if the UK sends out a signal it's easy to come "more people will die in the water".

There has been a public outpouring of sympathy in the past few days. But that may well not last, and voters' appetite for large numbers of new arrivals is unlikely to be strong. Particularly when councils are already warning that they'd struggle to cope with the costs.

And remember, this government has already used up significant amounts of political capital promising to get immigration down, missing its own target again and again, but continuing to stick by it.

In the short term, David Cameron has made the politically inevitable choice.

But this may make some of his own long term ambitions harder to achieve.