Angus Robertson follows up by saying there are concerns that women might have to prove that their pregnancy was a result of rape - and urges the PM to "think again" about the proposals. David Cameron assures him that the government will look very carefully at the matter.

SNP Westminster leader Angus Robertson uses his first question to the PM to press him over plans to limit child tax credits to the first two children. He raises concerns about cases where a woman fall pregnant as a result of rape. David Cameron says he was happy to look at this to make sure the government gets it right, saying it is not their intention to "penalise people who have been treated in this way".

David Cameron has the final say in these exchanges - and repeats his defence of changes to trade union political levies. "I thought she was the moderate one", he says of Ms Harman, adding that he thought it was the leadership contenders who were heading off to the left.

On to the government's trade union reforms, Harriet Harman seeks a guarantee that changes to the political levy will not be pursued without cross-party support. The Labour Party always comes back to the trade unions, David Cameron replies. Defending the government's position, he says it's a simple principle - if you want to give money to a party it should be "an act of free will".

But Ms Harman contends that it's "one rule" for Labour and a different rule for the Tories. She says the government wants to attack workers' rights - and accuses the PM of acting in the interests of the party.

Harriet Harman slips up and calls John Bercow the deputy Commons Speaker - cue swift apology. Addressing David Cameron she says: "I don't need to be patronised by the PM about not understanding the minimum wage. We introduced it," she says - before quoting the IFS as saying millions of families would be worse off as a result of the Budget measures.

Harriet Harman says Labour agrees on the need to cut the deficit but questions "what kind of government" would do it by taking money from the most vulnerable, citing changes to Employment and Support Allowance. David Cameron says Labour hasn't fully grasped the importance of the National Living Wage - saying it will help families. He then takes aim at Labour for being divided over whether or not to support some of the welfare reforms announced in the Budget speech.

Changing subject, Harriet Harman criticises the latest unemployment figures and the Budget - and says cuts to tax credits will hit low income families hardest. David Cameron says the latest unemployment figures are "disappointing" - but says there is some good news in some of the figures, including on long-term unemployment and youth unemployment - which are both down. On the Budget, he hails proposals to increase the National Living Wage.

Harriet Harman says there's wider geo-political significance to the Greek crisis with Russian President Vladimir Putin "waiting in the wings". David Cameron agrees. He says the UK is a friend and ally of Greece. While it's not for Britain to bailout Greece and eurozone countries, there would be a case for offering humanitarian assistance if Greece left the EU, he argues.

David Cameron says the UK talks to the IMF on a regular basis, adding that the point the IMF is making about debt relief "must be right". He says it's in the UK's interests for the eurozone to resolve these issues, and "quite fast".

Acting Labour leader Harriet Harman stands - and smiles as Tory MPs cheer her and wave their order papers (presumably as a result of her decision to back certain Budget measures). As it quietens, she presses the PM over the Greek debt crisis. The agreement must be fair to the Greeks and creditors, she says - but cites IMF concerns about the deal's sustainability. Has George Osborne spoken to the IMF about this?