Q. What is the EU Reform Treaty?
A. The agreement which replaces the draft European constitution. This was rejected by Dutch and French voters in 2005. EU leaders felt a new way of working was needed given that the Union is now made up of 27 members, hence the Treaty of Lisbon.

Q. What's all the fuss about?
A. While the official line of the various governments is that the agreement is a traditional amending treaty, some critics, notably the Tories, believe it is essentially the same document - a constitution by another name - and is yet another step towards European integration. Therefore, it is argued the UK Government should honour its election pledge and hold a referendum.

Q. So is it the same or not?
A. Here is the rub: while the treaty contains some of the key points of the draft constitution, it does not contain others.

Q. So what has it kept in?
A. First, the idea of a president of the European Council, who will serve for two-and-a-half years. He or she will replace the current system of a rotating presidency, which is taken by a host member state itself for six months - currently Portugal.

Second, the creation of a High Representative on Foreign Affairs, combining the roles of the EU foreign affairs supremo and external affairs commissioner to give the Union more influence.

Third, from 2014, a smaller Commission with fewer commissioners. Fourth, a reweighting of votes and the removal of some national vetos in 50 policy areas to ease decision-making. Fifth, new powers for the various European bodies on such topics as justice and home affairs, giving the EU a legal personality that will allow it to sign international treaties.

Q. So what has it left out?
A. While the draft constitution sought to replace all previous treaties, the new agreement simply changes the previous ones. Moreover, it drops all references to things like the EU flag and anthem.

Q. Given that Gordon Brown has signed the treaty, does that mean the UK has agreed to everything in it?
A. No. Britain's famous "red lines" means that it has secured various opt-outs such as on social policy, judicial and police issues, foreign and defence policy, and social security matters. Critics, however, warn these might not last forever.

Q. What happens next?
A. All 27 EU member states are due to ratify the treaty next year, and it is expected to come into force in 2009. Most will ratify it through their parliaments, though one state, Ireland, is constitutionally bound to hold a referendum on the issue.