Stay tuned for live coverage at 1200. A Budget live blog will follow at 1230.
1201: And we're off. Brown starts with condolences for the fallen. The first question from Mike Penning is a punchy one: when did the PM realise he "mislead" the Chilcot Inquiry? Before or after? Brown responds by pointing out that defence spending has risen in real terms over the last 12 years, if not every year.
1203: A planted question gives Brown to opportunity to list Labour's "fairness measures". He says they would never have been put forward by George Osborne.
1204: Cameron starts by saying that he'd "like to clear up a few issues". Laughter from the Labour benches, for some reason. He asks whether Brown would ask workers to "cross the picket line" outside the Treasury.
1205: Brown congratulates the Camerons on SamCam's pregnancy.
1206: Cameron asks Brown whether the government will publish information about the gold sales at the beginning of the New Labour years. Brown immediately starts saying that the Tories have no answers. The Labour benches roar him on.
1208: Cameron follows up with a similar question about taxes on pensions: why not publish information? Unsurprisingly, Brown is full of partisan bluster. He says that he has no problem with relvealing anything about his record, adding that the Tories sould release information about Lord Ashcroft. Hm.
1210: Oh dear, it got to that stage - where Brown is asking questions about "what the Tories would do". Far more heat than light being generated today. The Labour and Tory benches jeer and cheer en masse.
1212: It's Clegg's turn to try and cut through Brown's bluster now. He says that the Lib Dems proposed measures to restrict lobbying, but they were resisted by other parties. The other beches erupt with shouts of "Michael Brown".
1213: Brown drones on about the meagre parliamentary reform measures his government has presided over.
1214: Clegg says, quite rightly, that Labour had 13 years to sort this. Quite an impressive performance from the Lib Dem leader.
1218: Graham Brady asks whether Brown would rather be remembered for destroying pensions or rising council tax. Brown reponds that he'd like to be rememeber for "the next election". He sits down with aplomb, and smiles smugly at Alistair Darling. Well done, Gordon, you told a joke.
1221: Brown says that government is takign the threat of mephedrone "seriously".
1222: The House has become more sedate now. Brown faces another question on pensions - which seems to be a Conservative theme today. It makes sense: this is an issue which affects so many, but which doesn't get as much attention as it deserves.
1226: We're into the last couple of questions, but let's hop over to Coffee House's live Budget blog.
QUICK VERDICT: this was an even less enlightening session that usual. Cameron didn't hit home with his attacks, Brown got stuck in a deeply partisan groove. Clegg was probably the best performer, even if the Lib Dem's holier-than-thoh shtick can be grating.