Stay tuned for PMQs coverage from 1200.
1200: And here's Brown, fresh from his meeting with Obama. He welcomes the US President on "behalf of the people of the UK". And then: "I'm proud that we're hosting the G20 meeting".
1202: Brown bats off a question about Lord Myners by effectively saying that the matter of Fred Goodwin's pension is in the hands of the UKFI.
1203: Good start from Cameron. "Before getting on to the G20, I'd like to bring up the matter of MPs' expenses. MPs may groan, but I'm fed up with politics being dragged through the mud." Cameron calls for quicker reforms and a meeting between the party leaders. This is encouraging stuff.
1205: Brown says he's happy to meet the other party leaders, but that they'll still have to wait for the end of of the inquiry nonetheless.
1206: Cameron pushes the issue harder. "We don't need another review". And then points out, rightly, that the last review was largely ignored by Brown. Brown replies similarly to his last answer. Clever from Cameron: despite Brown's claim that he'll meet with Cameron and Clegg, this still makes it look as though Brown doesn't have the political will to act swiftly and decisively.
1207: Now onto the G20. Cameron asks for assurances that barriers won't be put up to free trade.
1209: Brown just waffles on for a couple of minutes about why this G20 meeting is so "important".
1211: Cameron calls for progress towards a complete Doha agreements. Brown: "We will push forward on trade and on other measures ... there is no-one coming to London who has a policy of do-nothing." Groan.
1212: Cameron plays his trump card: "There's a person already in London saying that you can't spend any more money, and that's the Governor of the Bank of England." Brown says that the Tories "don't understand" and launches, again, into a "do nothing" diatribe.
1214: Cameron's got all the right responses today. He tears into the "do nothing" attack, saying that "it's not working ... since the PM started saying it, we've gone up and he's gone down." And then: "It's all about creating another political dividing line".
1215: Brown's response is unedifying. He claims that Cameron's only concerned with "politics" and hasn't mentioned "people," before launching into a diatribe about how the Tories would cut child benefits, pensions etc. etc. Erm, wasn't Cameron's point - rightly - that Brown is being too political? The Tory benches are in uproar. This is getting quite heated.
1217: Clegg now, and he's in fiery form - saying that Brown must "practise what he preaches" on the global stage. Brown responds by bringing in back to the "do nothing" Tories.
1218: Clegg has Brown looking flustered, as he pushes this "practise what you preach" attack. Like Vince Cable last week, he says that the VAT cut was a waste.
1223: Backbench questions. David Winnick calls for a better "system of allowances". More on Icelandic banks and carbon capture.
1225: David Heathcoat-Amory lays into Brown for selling our gold reserves, and calls for an apology in light of the fact that gold prices are now 4 times higher. Brown stutters that "many countries were diversifying at the time ... and we invested in Euros, which have gone up in value!" Hm.
1229: Questions on unemployment, community policing and cancer care. Brown says that a programme to tackle unemployment will be announced soon - looking ahead to the Budget, methinks.
1231: That's it. Verdict shortly.
VERDICT: While Cameron didn't deliver any killing blows, I think he came out comfortably on top - mainly by positioning his party on the right side of the expenses dividing line. Besides, it was good to hear him say what quite a few Labour people think about the "do nothing" attack.