Ratification of the European reform treaty is set to provide the government with one of its biggest legislative headaches, with critics stepping up their referendum calls.

Ministers expect the ratification process to take up to three months, with detailed scrutiny in the Commons already promised by the prime minister.

The government also faces difficult votes in the Lords, where Labour lacks a majority.

But the Liberal Democrats have not given their backing to Conservative calls for a referendum on the treaty, saying any vote should be on the wider issue of Britain's EU membership.

The bill is expected to be introduced after the Christmas break, with the aim of having it on the statute book by the end of March.

Tory leader David Cameron has so far declined to say if he would seek a referendum on the treaty once it has been ratified.

And Gordon Brown will be hoping that the issue slides out of the headlines in the months after ratification.

The government believes detailed parliamentary scrutiny of the document will prove that a referendum is not required.

And the prime minister has pledged the "fullest possible parliamentary debate" on the issue.

The Conservatives, meanwhile, aim to prove that ministerial 'red lines' will not prove enforceable in practice.

In so doing, they argue it will be clear that the government has breached its promise to hold a referendum on the previously planned constitution, which is seen as being similar to the treaty.

Labour MPs will not be given a free vote on ratification, but chief whip Geoff Hoon has said he is "not anticipating a big Labour rebellion".

A second piece of legislation, the European Communities (Finance) Bill, will also be introduced in the new parliamentary session.

It establishes new financial procedures to work with the EU's system of 'own resources', the process through which national governments finance the annual European budget.

The legislation will allow the UK to make payments to the EU directly from the Treasury's 'consolidated fund'.