LONDON (Reuters) - Conservatives, who want to claw back a host of powers delegated to the EU, opted on Tuesday to leave key justice powers in Brussels after their pro-EU coalition partners and police said national security was at risk.
Home Secretary Theresa May said Britain wanted to remain part of 35 pan-EU measures including the European Arrest Warrant, a system that allows the transfer of suspects between member states.
Prime Minister David Cameron, trailing in the polls, is under pressure from Conservative Eurosceptics to take a harder line with Europe or even leave a 28-nation bloc that they see as a threat to Britain's sovereignty.
He has said he will try to secure a "repatriation" of powers from the European Union across all areas of government and then hold a referendum on Britain's membership of the bloc, provided he wins the next election, due in 2015.
The opposition Labour Party taunted May in parliament, saying the justice deal was "hardly a triumph of repatriation". Conservative Eurosceptic Jacob Rees-Mogg called it a surrender of sovereignty.
May said the government had listened to criticism that opting out of the justice measures would hamper criminal investigations across Europe.
"Some of these measures covered by this decision are important tools which they need to protect the British public," she told parliament.
Britain's right to repatriate a package of justice powers was agreed by the previous, Labour government before the signing of the Lisbon Treaty, the agreement that reformed the EU's constitutional framework.
After formally opting out of all of the legislation, comprising more than 130 powers, Britain must now ask the EU to allow it to opt back into the areas it wants to adopt.
The European Commission said in a statement: "At first sight, it appears that the UK has looked at the opt-ins in a pragmatic way."
Labour portrayed May's announcement as an early failure in Cameron's wider attempt to win back powers from Brussels.
"This is hardly a triumph of repatriation," said Labour home affairs spokeswoman Yvette Cooper, pointing out that some of the measures where Britain has chosen to retain national responsibility were defunct and others had never been used.
"The Home Secretary has tried to play Britannia, clothing herself in the union jack (flag), parading powers that she is repatriating from Brussels. The truth is, she isn't wearing a flag, it is simply a fig leaf."
Cameron's coalition partners, the pro-EU Lib Dems, welcomed the decision to keep Britain in the arrest warrant system.
"They were proposing to abandon key European crime-fighting measures," said Sarah Ludford, a Liberal Democrat member of the European Parliament and justice spokeswoman.
(Additional reporting by Claire Davenport in Brussels; Editing by Kevin Liffey)