Foreign Secretary William Hague launched a late bid to see off a backbench Tory eurosceptic rebellion by insisting a promise of referendums on EU treaty changes were "a massive advance for national democracy".
Critics are set to push amendments seeking to strengthen protections contained in the The European Union Bill when it is debated in the Commons on Tuesday amid fears the powers are too open to challenge.
Writing in the Sunday Telegraph, Mr Hague defended the package and accused Labour of seeking to "deny the British people their new democratic power".
The new law would be "the strongest defence of national democracy put in place anywhere in Europe", he said.
"Not only will parliament now be given a full say over all kinds of treaty change but any change that hands powers to the EU or extends its control over any area of policy will also be subject to a referendum.
"It is a massive advance for national democracy."
Ministers would only have discretion not to put changes to the country in "a few minor areas" and even then would need to persuade parliament and the courts, he said.
Shadow foreign secretary Yvette Cooper said: "Even the Foreign Secretary must know this Bill is a dog's dinner.
"This Bill is about failed Tory party management, not the issues that matter for Britain in Europe. Instead of concentrating on things like growth, exports or cross-border crime, William Hague is wasting time trying and failing to keep his eurosceptics happy.
"Even worse, the Bill is so badly drafted and contradictory that it could lead to a lawyers' paradise where important decisions happen in court rather than parliament."
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