Referendum vow over UK rule in EU prosecutor
Future UK governments will have to hold a referendum if they want to get involved in a Europe-wide prosecuting authority, a minister has told MPs.
Europe Minister David Lidington offered the "referendum lock" as MPs debated the European Union Bill.
The European Union Bill is meant to prevent the handover of further powers to Brussels without a public vote.
But Labour say it is a "political gesture" to appease Eurosceptic Tories. The Commons debate will continue later.
On day three of the bill's committee stage on Tuesday, Mr Lidington said the government had already explicitly ruled out taking part in a European Public Prosecutor's Office in the coalition agreement.
But he said the changes to the EU Bill "would ensure that a referendum would be required in all cases before the United Kingdom could join the European Public Prosecutor or an extension of that prosecutor's powers, whether that decision was taken before or after that prosecutor had been set up or before or after the powers of that prosecutor had been extended".
Former Conservative Cabinet minister, and leading Eurosceptic, John Redwood said: "I'm very grateful for that concession which does improve the bill."
But he added: "Can you not understand that most people think criminal justice is essential for the sovereignty of themselves in parliament and that this same provision should apply for all opt-ins under the criminal justice provisions.
"Why won't you concede that?"
Mr Lidington said opt-ins on justice and home affairs would be debated on Wednesday.
He also reassured MPs that the government would not ask the public to vote again on an EU treaty change transferring more powers to Brussels if they had earlier rejected it.
"I simply don't believe that any British government is going to be defeated at a referendum and then come forward and say to its electorate 'no, you've got it wrong, let's dissolve the people and have a new one'. This really doesn't make political sense," he told MPs.
Shadow foreign minister Emma Reynolds, for Labour, said the EU Bill was solely designed to appease Conservative backbenchers - something she said it had failed to do.
"If the government are so committed not to transfer power then why do we need this bill?," she asked MPs.
"Is it that their own backbenchers don't trust them to keep to the text of the coalition document. This bill is unnecessary, it's a dog's breakfast, it's a political gesture to calm the fears of the Eurosceptics of those sitting behind the minister."
Lib Dem President Tim Farron said that although, on paper, the Bill was not necessary, MPs did need to "make a statement which guarantees, if you like, that this place is sovereign and that the public's power over our membership of the European Union is ultimate and paramount".
The Bill includes a "sovereignty clause" which is meant to assert the primacy of the Westminster parliament - but some Conservative backbenchers have said it does not do enough to claw back power from Brussels.