The PM's statement to parliament is expected to include the announcement of a further cut in the number of British troops in Iraq, and an aid and investment package to boost the Iraqi economy.
3.30pm
Mr Brown starts by paying tribute to seven members of the armed forces who have died since April and also the 18 who have died in Afghanistan over the same period.
The prime minister reads out all their names.
He says they died doing "vital work".
The PM says that the strategy is political reconciliation, security and economic reconstruction, founded on the UN mandate.
He says there is unanimous support within the UN despite differences over the decision to go to war in 2003.
Mr Brown says the future depends on political reconciliation which he discussed with Nouri al-Maliki on his trip to Iraq last week.
He says Iraq's neighbours must provide support and not provide funding or assistance to terrorist groups.
He renews his call on Syria and Iran to halt support for terrorists and says they must shore up their border controls.
3.35pm
The PM pays tribute to the steadfastness of our coalition partners, all 26 of them. He refers to the report by General David Petraeus, the US commander in Iraq, and Ryan Crocker, the US ambassador in Iraq.
Mr Brown says the UK has helped train more than 13,000 Iraqi troops.
He says 15,000 police officers have also been trained in southern Iraq and security services stand at over 30,000 now and that number will rise to 35,000 by June next year.
The PM says that all decisions in Iraq are based on the assessment of military commanders and conditions on the ground and that three of the four areas under British command were transferred following an assessment of those conditions.
Mr Brown says that the armed forces are moving to "overwatch" in the remaining area, Basra.
That involves securing the supply routes but will move later to training and mentoring from next spring.
The number of troops will go down to 2,500 next spring.
At the start of September the figure was 5,500.
A further decision will be made in spring on further possible reductions in numbers.
Mr Brown pays tribute to our civilian and locally trained staff in Iraq.
He announces a new policy that will see existing staff employed by the forces for more than 12 months be able to apply for a package of financial packages to help resettlement in Iraq or abroad. He says details will follow this week.
3.40pm
A Basra development fund is being launched in Iraq with $30m to provide assistance for small businesses.
Mr Brown says the Iraqi deputy prime minister has announced $300m for economic development in Iraq.
He's moved on to military hardware and says the government is placing an order for another 140 armoured vehicles.
The government will also double the number of computer terminals for members of the forces to stay in touch with friends and families.
The PM moves on to the Middle East peace process and says there is the best prospect of a final status settlement since 2000.
3.45pm
He welcomes Tony Blair's work as Middle East peace envoy to the quartet.
Mr Brown is paying tribute to the armed forces once more. He says that "the scale of their achievement will always be remembered".
David Cameron, the Tory leader, welcomes the statement and says such statements should always be made in the Commons (a swipe at the PM for his announcement on the reduction of troop numbers made in Iraq last week).
Mr Cameron asks about the reduction in troop numbers, the goals of remaining troops and the prospects for political reconciliation.
He asks if the Iran-Iraq border can be secured, whether the PM is satisfied that troop reductions will not jeopardise the safety of remaining British forces and about laws governing oil revenue distribution and whether he agrees there should be a permanent group engaging with numbers.
Mr Cameron asks whether, now the troops are coming home, we can have a full public inquiry.
He also wants a full quarterly, at least, report on Iraq or Afghanistan.
3.50pm
The Tory leader asks the PM whether he will admit his so-called mistakes in respect to his statement announcing cuts in troop numbers during the Tory party conference while in Iraq last week.
Mr Cameron says it is "not an acceptable way" for the prime minister to behave.
Mr Brown says he will work hard for political reconciliation and says there is a UN group working with Iraq's neighbours.
He says that the overwatch phase still gives British troops the ability to re-intervene in the first stage and they will eventually move to the second stage of overwatch when their main role will be training and mentoring Iraqis.
3.55pm
There will be a reduction first to 4,500 troops and then another reduction to 4,000.
Mr Brown says this is not the statement he made in Iraq last week.
There will be an additional 500 troops outside Iraq but he won't say where, for security reasons.
Mr Brown says he makes "no apology" for visiting British troops in Iraq, prompting a lot of noise in the Commons.
Sir Menzies Campbell, the Liberal Democrat leader, is up, and paying tribute to the armed forces - but he says they were given "an impossible task" in Iraq.
He welcomes the change of heart in respect to interpreters and other people working for the forces but wants to know the number of people who will benefit and what the terms will be.
Mr Campbell says Britain's involvement in Iraq has been a "catastrophe" and the presence of British troops no longer serves any useful purpose.
Sir Menzies says Britain has fulfilled its obligations to Iraq after four and a half years and that the UK's obligation now is to our young men and young women.
He claims the British presence in Iraq is jeopardising the mission in Afghanistan.
4pm
Mr Brown retorts that the Lib Dems should recognise that we also have international obligations including protecting the Iraqi people under UN resolutions.
He says there are some 450 people who have helped the armed forces who may qualify for resettlement assistance.
The PM insists decisions have been made on military advice. He claims Sir Menzies sometimes accuses the government of having too many troops and at other times having not enough.
Frank Dobson, the former health secretary, says that the opposition should remember it supported the war and welcomes reductions in troop numbers.
Mr Brown says there will be no "artificial" timetable for reduction in troop numbers.
The PM is asked again about his statement in Iraq last week and accused of not admitting that some of the troop reductions he referred to had already been announced and some members of the armed forces were already home.
4.05pm
Sir Malcolm Rifkind, Conservative MP for Kensington and Chelsea, says that Mr Brown was the second most powerful member of the Blair government and should accept his share of responsibility for the "greatest error in British foreign policy in recent times".
Mr Brown says even if Sir Malcolm disagreed with the decision to go to war he should support the steps to support the transition towards democracy in Britain.
The PM says the reduction in troop numbers (from 45,000 in 2003) is only because the Iraqis are capable of taking over security and they will not leave the country prematurely.
4.10pm
Mr Brown is asked about Alan Greenspan's comment that the Iraq war was "all about oil" and whether he will be discussing the issue with with the former chairman of the US Federal Reserve.
Once again he is asked about the numbers of interpreters and the like who might benefit from the resettlement scheme.
He says there are 200 who have finished their work and a further 250 who may qualify and disagrees with Mr Greenspan.
Kenneth Clarke, the former Tory chancellor, says that re-intervention by British troops would not be a realistic course of action after today, and that Mr Brown is trying to get them out of Iraq as soon as possible for political expediency.
Mr Brown says the troops are serving a purpose by their presence. He wants Mr Clarke to look at the progress that has been made and says they are helping the Iraqis build a local democracy.
Jeremy Corbyn (Lab, Islington North) asks about the support given to Iraqi refugees in Jordan and Syria and asks that Iraqi asylum seekers are not sent back from the UK.
4.15pm
Mr Brown accepts there are large numbers of Iraqis outside Iraq but says they are outside the country because Iraq was safe but the situation on the ground is changing.
Charles Kennedy, the former Lib Dem leader, asks if Mr Brown agrees that the basis of our very presence in Iraq is the problem - namely that we never got a second UN resolution.
Mr Brown says intervention in Iraq is now covered by a UN resolution and about supporting the prosperity and security of the Iraqi people. He wants that to be "common ground" in the Commons.
Don Touhig (Lab, Islywn) says the opposition is engaging in "party political posturing" rather than celebrating the withdrawal as it should, and says it is only because of the troops' achievements on the ground that they are now able to begin pulling back.
Sir Patrick Cormack (Con, Staffordshire South) calls for reassurances that returning troops are properly supported and housed.
Mr Brown says much more needs to be done but they have set cash over the next 10 years for funding housing for troops.
4.20pm
Nicholas Soames (Con, Mid Sussex) asks what reserves will be available to help the troops as the numbers go down.
He unfavourably contrasts Mr Brown's behaviour over choosing not to call a snap election with the courage of troops in Iraq.
Eddie O'Hara (Lab, Knowsley South) says that if British forces were to "cut and run" it could jeopardise the remaining numbers.
Ann Winterton (Con, Congleton) asks if the cost of the 140 new armoured carriers will be borne by the Treasury rather than coming from the armed services budget.
She also asks if they will be designed to ensure maximum protection for troops.
Mr Brown says it will cost £120m and is being met by the defence settlement.
4.25pm
Anne Snelgrove (Lab, Swindon South) says the announcement demonstrates that giving Iraqi people responsibility for their own determination is the right policy and should be recognised by others.
Keith Simpson (Con, Mid Norfolk) asks if the defence secretary, Des Browne, was aware of Mr Brown's statement in Iraq before he made it.
The PM says that all figures were agreed. (There were newspaper reports that Mr Browne was not aware of it in advance and was angry about it.)
4.30pm
Andrew MacKinlay (Lab, Thurrock) says we are "too nice to Iran".
Mr Brown says there has been success in policing the border and coalition troops will continue to do so.
Sir Peter Tapsell (Con, Louth and Horncastle) asks the PM why he did not support the late Robin Cook in opposing the invasion and occupation of Iraq.
Mr Brown says achieving success in Iraq will make a "huge difference" to what is happening in the rest of the Middle East.
William Rennie (Lib Dem, Dunfermline and Fife West) says that our troops are "part of the problem" and not the solution in Basra.
Mr Brown says British forces are an essential presence in bringing about a "calmer" situation.
The PM says he hopes to announce more generous compensation for members of the armed forces who are injured.
And that's the end. Thank you for joining me; stay on the site for reaction.
