We think it is quite wrong for the government to be pushing this through when the Irish public in their referendum have just rejected this treaty

Shadow foreign secretary Francis Maude

European Commission President Romano Prodi has suggested enlargement might go ahead anyway - but Mr Straw told the BBC that all EU states must agree to the treaty before it could come into force.

He was speaking ahead of a debate on the Nice Treaty in the House of Commons on Wednesday afternoon.

"Treaties like this require 15 member states, all member states to ratify them, so if any one fails to ratify it, it doesn't come into force," Mr Straw told Radio 4's Today programme.

'No other treaty available'

"Theoretically you could have a different treaty in order to ensure enlargement.

"But there isn't a different treaty available, it's the Nice Treaty."

Mr Straw said that Mr Prodi now realised he was wrong in his suggestion about enlargement.

The alternatives now were a new treaty to ensure enlargement or, more likely, "discussions with Ireland about whether there are things at the margin which could assist the Irish people in coming to a 'yes' vote".

Nice Treaty was rejected in a referendum in Ireland

Mr Straw continued: "The one thing nobody wants in Europe is that the Nice Treaty ... should somehow be stopped in its tracks."

But shadow foreign secretary Francis Maude argued that the government was ignoring public opinion by pressing ahead with ratification.

"We think it is quite wrong for the government to be pushing this through when the Irish public in their referendum have just rejected this treaty," said Mr Maude.

Crack down

Mr Straw used an article in Wednesay's Daily Telegraph to set out what he saw as the advantages of enlargement, with plans for 12 Eastern European states, Malta and Cyprus to join the Union.

Increased trade would boost Britain's GDP by up to �1.75bn a year, according to Mr Straw.

The move would also help crack down on organised crime, drugs trafficking, illegal immigration and pollution, he said.

Under the Nice Treaty, qualified majority voting would replace unanimous decisions in several areas.

But Prime Minister Tony Blair and former foreign secretary Robin Cook had ensured Britain retained a veto in key areas, such as taxation, while introducing the possibility of much needed reform in others, Mr Straw said.