The prime minister can expect a hostile reception as he makes a statement to the House of Commons on the new EU reform treaty that was agreed on Friday.
The prime minister is happy that the "red lines", initially agreed by his predecessor, Tony Blair, offer Britain protection from undue inference by European institutions.
And he is adamant that the retained controls over foreign, social and security policy mean that the treaty is substantially different from the failed constitution, so that Labour's 2005 election pledge to hold a referendum is no longer relevant.
But amid claims that the red lines are not enforceable and support for a public vote from the Conservatives, trade unions, some Labour backbenchers and significant sections of the media, he can expect some tough questions today.
3.30pm
We're off. Mr Brown says it was agreed at the Lisbon summit that aside from the treaty global issues including climate change are the priorities.
Now he says the constitution has been abandoned - to jeers from the Tory benches.
He invites the house to study the protections secured by the government, including a safeguard for the UK on the charter of fundamental rights.
This will prevent anything in the charter "challenging or undermining" any rights available in UK law.
Mr Brown says the safeguards are enshrined in legally enforceable protocols.
3.35pm
He refers to the opt-ins and says the new treaty gives the government the ability to protect "the fundamentals of our common-law system".
"We can choose to participate in any and every measure but we cannot be forced to do so," says Mr Brown.
The opt-ins refer to home affairs and security, he says.
Mr Brown says the inter-governmental basis is "unchanged".
It does not affect foreign policy; there is no role for the European parliament in decision-making, says the PM.
Mr Brown says that EU foreign policy will continue to be decided by "unanimity".
On social security the UK has secured a veto to prevent change, including the scope and financial structure of the social security system.
3.40pm
The new position of president of the European Council - held for two and a half years - is the servant of the leaders of EU countries, Mr Brown insists to some heckles.
European flags, anthems and mottos - elements that were in the failed constitution - have been abandoned, says Mr Brown.
He will only sign the treaty if the protections secured by the government are included, he insists.
The speaker scolds the opposition for their persistent heckling.
Mr Brown starts again and insists that there will be no more moves towards qualified majority voting - unpopular because it means no one country has a veto on a given issue - without a vote in the House of Commons first.
He says there will be no more institutional change for "many years".
The prime minister says it is right that the EU focuses on global priorities rather than pursuing further institutional change.
Those priorities include closer EU-US links and reforming the EU budget.
He wants an agenda that delivers economic prosperity and jobs.
He claims the protections agreed "defend the British interest", and commends the statement to the house.
3.45pm
David Cameron, the Tory leader, stand up to say that the PM has described the 2005 Labour election manifesto - which promised a referendum on the EU constitution - as an issue of trust.
He says that Mr Brown, in his statement today, could not bring himself to say "the 'R' word" once. "Let the people decide," urges Mr Cameron.
Mr Cameron rubbishes the PM's claim that there will be no institutional changes for 10 years, arguing that there will be change every year under the treaty.
He quotes other leaders who have claimed the treaty is substantially the same as the constitution.
Mr Cameron makes reference to the report by the Commons European scrutiny committee, which said that the reform treaty is "substantially equivalent" to the constitution.
He claims the "red lines" are purely presentational.
Someone on the Tory backbenches is getting a bit excited, continually shouting "Ahhh!" in a high pitched voice after Mr Cameron concludes each of his points.
Mr Cameron says "these red lines will basically leak like a sieve".
Mr Brown is smiling as Mr Cameron claims he will not hold a referendum because he knows he would not win it.
The Tory leader says the PM is "betraying" the British people.
He wants Mr Brown to tell him whether Labour MPs will be given a free vote on whether to hold a referendum.
3.50pm
Mr Brown notes that Mr Cameron did not mention any of the EU's long-term priorities in his response. He points out that the Tories voted against a referendum on the 1992 Maastricht treaty.
The PM says "sometimes I think that he [Mr Cameron] doesn't listen to me". He is sounding like an exasperated parent.
Mr Brown calls on Mr Cameron to read the protocol referring to the charter of fundamental rights.
He also makes repeated reference to passarelles, a rather obscure piece of EU jargon.
3.55pm
He says that the Tories are not only against the new treaty but want to renegotiate Britain's membership of the EU and the social legislation.
Mr Brown insists that would be "unacceptable to business and to the British people".
Now, the PM is referring ominously to the Tories' "friends" in Europe - his point is that the Conservatives don't have many.
The speaker once more calls for calm.
"He [Mr Cameron] has no friends in Europe," says Mr Brown. "We will defend the British interests."
There are cries of "more!" and now the acting Liberal Democrat leader, Vincent Cable, is speaking.
He says: "We do believe there should be a referendum," prompting cheers, but then adds that it should be on EU membership as a whole - prompting groans.
The Punch and Judy Commons is clearly still alive and well.
Mr Cable says the vote should be on all the changes that have occurred since Britain joined the EU.
He says a vote would force Mr Cameron to say whether he is for or against Britain's membership of the EU.
Mr Cable asks why Mr Brown did not do more to promote the principle of subsidiarity.
He criticises Peter Mandelson, the EU's trade commissioner and former Labour minister, for being concerned with protectionist measures and then asks the PM for a timetable for reform of the controversial common agricultural policy.
4pm
Mr Brown says he hopes negotiations with Turkey over membership will start soon.
He agrees with Mr Cable that it's time to have a debate about Britain's future in the EU.
The PM expresses his pleasure at the fact that Lib Dem leadership contenders Nick Clegg and Chris Huhne both agree that the treaty is not a constitution.
The PM is being asked to confirm that the new representative for foreign affairs will not be an EU foreign minister.
Mr Brown insists foreign policy will remain intergovernmental and that there will be no removal of Britain's seat at the UN security council.
4.05pm
Next he has asked how the justice and home affairs opt-ins will work at the end of five years.
Mr Brown says measures will move from being intergovernmental to be part of the treaty itself but the government will have the right to opt out at that point.
Sir Gerald Kaufman (Lab, Manchester Gorton) refers to the election manifesto commitment for a referendum but says that it only referred to a constitution.
Mr Brown says the amended treaty is "quite different" from the constitution.
Iain Duncan Smith, the former Tory leader, claims that the European courts will find in favour of the EU as a single legal personality, eroding the "red lines", and the protections they offer.
Mr Brown rejects his comments, asking why the Tories supported a referendum on the treaty when they did not support one on Maastricht (although IDS was a leading Maastricht rebel).
4.10pm
Sir Stuart Bell (Lab, Middlesbrough) says the opposition should support Mr Brown's achievements in defending the British interests.
The PM says at some point the Tories will have to come to terms with the fact that EU membership benefits Britain.
Mr Brown claims EU membership has created three million jobs.
David Heathcoat-Amory (Con, Wells) claims the PM is damaging democracy.
Mr Brown says there would be a referendum on joining the EU or on the old constitution but none is necessary for the treaty.
Michael Connarty, the chairman of the European scrutiny committee, says Mr Brown is quoting its report accurately and asks if there will be detailed procedures helping the house to decide whether to opt in or out on various issues in the next five years.
Mr Brown is pleased the ESC recognises the treaty Britain is signing is "different in its consequences" for Britain as opposed to other countries.
Charles Kennedy, the former Lib Dem leader and new president of the European Movement lobby group, says that the most common complaint by people is that there not being given unbiased, clear information on the treaty.
He suggests more information should be made available through the education system.
The PM claims the public will come to the view that the government has done the right thing to protect British interests.
Peter Bottomley (Con, Worthing West) asks if the British people will be allowed to decide on the treaty.
No surprise: Mr Brown says no referendum is necessary.
4.15pm
Dawn Butler (Lab, Brent South) asks if the PM agrees with the trade unions that the government should not put jobs at risk.
Mr Brown doesn't want jobs to be put at risk by not signing up to the treaty.
In response to another question about legal advice on the "opt-out" from the charter of fundamental rights Mr Brown insists the charter does not create new rights.
David Winnick (Lab, Walsall North) condemns xenophobia, which he says is driving opposition to the treaty.
Sir Malcolm Rifkind (Con, Kensington and Chelsea) asks about the Europe minister's comments to the European scrutiny committee that the protocol on the charter of fundamental rights is not an opt-out.
Mr Brown insists the protocol is "part of the treaty and legally binding".
4.20pm
Chris Bryant (Lab, Rhondda) asks about liberalisation of the energy markets, particularly in France.
Mr Brown says on energy and intellectual property rights Britain will benefit from the treaty.
He reads a letter from Centrica praising the treaty in so far as what it can do for energy liberalisation.
Bill Cash (Con, Stone) claims people have been denied a referendum since 1975.
The PM reiterates he would hold a referendum on joining the euro, which prompts laughter for some reason.
The speaker intervenes once more.
Mr Brown once again claims the treaty is quite different for Britain than for other countries.
The PM is asked about what impact the treaty can have on regional inequalities.
Mr Brown says the regions are receiving benefits from membership of the EU and three million jobs depend on trade relationships with Europe.
Sir Nicholas Winterton (Con, Macclesfield) asks if the PM believes in truth, honour and honesty.
He cannot have expected Mr Brown to say "no" to that one.
4.25pm
There is a question on whether there will be sufficient time in the Commons to debate the "red lines" in detail.
Mr Brown says there will be.
Next up is the common fisheries policy. Angus Robertson (SNP, Moray) claims this was a "red line" issue for Scotland but Mr Brown simply says the policy has not been changed.
Nigel Waterson (Con, Eastbourne) wants to know the percentage of the original constitution the PM believes remains in the treaty.
The PM once again insists the treaty Britain has agreed to is different from that agreed by other countries.
Sir Patrick Cormack (Con, Staffordshire South) wants a commitment that the issue will not be timetabled.
Mr Brown merely responds that there will ample opportunity for the treaty to be debated.
He adds that Ireland is the only country that is having a referendum, as it is constitutionally required to do so.
The PM is asked about the beneficial impact of enlargement of the European Union. Mr Brown says everything will be done to integrate the new countries into the EU.
Andrew MacKinlay (Labour, Thurrock) says the time is coming when a referendum is needed, not on the treaty, but on membership of the EU. He is looking forward to arguing the pro-EU case.
He describes the Tories as having many members of the "flat earth society".
4.30pm
Mr Brown says as the debate continues he hopes people will see the benefit of continued membership.
And it is all over.
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