Speaker Michael Martin finally bows to increasing pressure and quits

He's gone, Michael Martin has finally bowed to demands for him to go and will announce at 2.30pm this afternoon that he is resigning as Speaker of the Commons.

There will be strong suspicions - no doubt denied - that Martin, a Labour MP, was finally pushed by Gordon Brown to take some pressure off the Government. MPs calling for his resignation said it will "lance the boil".

But get ready for the usual sickening expressions of gratitude for the Speaker this afternoon from MPs who yesterday were calling for his head.

This morning's decision - he's the first Speaker to quit since the 17th century - has come as a total surprise to MPs. Just 24 hours earlier, he was insisting he would oversee the radical reforms needed to restore public trust in the House of Commons.

He was due to meet party leaders – Brown, David Cameron and Nick Clegg - at 4pm today to thrash out a way forward. Now they'll use the meeting to deal with the niceties of his departure. The likelihood is that his deputy, Sir Alan Haselhurst, will take over as interim Speaker some time very soon, pending an election for the new Speaker.

Haselhurst, a Tory, would normally have expected to be a shoo-in in these circumstances, but he has been caught in the expenses mire too - he charged the taxpayer £12,000 for gardening bills on his Essex farm.

Questions will be asked about what made Martin change his mind? He had clearly lost the support of sufficient numbers of MPs from all sides, making it impossible to go on, and 23 had signed a Commons motion calling for him to quit. But it's unlikely this morning's torrid headlines persuaded him. He hated the press, and would never have given up the chair to become a media scapegoat.

That is why MPs believe it is far more likely a phone call from Brown's office did the trick.