MPs are to vote on government plans to ensure “significant” European Union treaties must be approved by a referendum of UK voters.
This would also apply to major changes made to existing treaties.
But ministers can rule out a referendum when they judge that the transfer of power to Brussels is “not significant”, which worries eurosceptics.
MPs will be able to raise concerns when the European Union Bill has its second reading in the Commons later.
The government says it has no plans to transfer sovereignty or powers to the EU in this parliament, as part of the coalition agreement between the Conservatives and Liberal Democrats.
Foreign Secretary William Hague told the BBC: “It’s a bill I’ve long wanted to present to Parliament, which says that if this government or any future government transfers new areas of power, or more competence to the European Union from the UK, then the people of the country must be consulted in a referendum by law.
“That of course is what I thought should have happened over the Lisbon Treaty during the Labour government, but this is putting it right for the future and saying the British people must be asked if their own rights or powers are being given away.”
But Labour have dismissed the legislation as a “sop” to Conservative eurosceptics, rather than a serious policy.
The cross-party European Scrutiny Committee has published a report attacking the government for not allowing it sufficient time to scrutinise the bill.
Its chairman, Conservative MP Bill Cash, said: “The European Union Bill is in its implications, and given the profound effect that the European Union has on the daily lives of the voters and the people of the United Kingdom in virtually ever sphere of activity, of immense importance and in many respects on a par with the original European Communities Act 1972.”
He added it was “essential that it is made clear that Parliament is the ultimate authority” in defining “the United Kingdom’s relationship to the EU”.
The bill did not address the “vital constitutional issue of the competing primacies of EU and national law”, the committee said, while the coalition had “purported” to include a “sovereignty clause”.
Under the legislation, ministers will be able simply to state whether the transfer of power from the UK to the EU is, or is not, significant enough to merit a referendum.
If they say a public vote is not needed, they will be able to make the change if they manage to pass an Act of Parliament to that effect.
The minister’s ruling could be challenged in the courts.
Broader changes to the UK’s relationship with the EU will have to be put to a national referendum.
Eurosceptics argue that the measures outlined do not go as far as the “referendum lock” outlined in the coalition agreement, which was to apply to any future transfers of power.
The government has already made clear there will not be a referendum on treaty changes suggested by the German Chancellor Angela Merkel, to establish a permanent mechanism to protect the euro, because the UK says that would only affect countries which use the single currency.
That will, instead, be subject to an Act of Parliament.
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