European police will be able to insist that Britons are put under surveillance and gain access to their DNA after the UK opted into controversial plans to strengthen co-operation.
Theresa May, Home Secretary, said the European Investigation Order (EIO) will "allow us to fight crime and deliver justice more effectively". But campaigners said it would give European police "free rein" to spy on Britons and could lead to disproportionate requests, with demands for the DNA of British tourists if there was a serious crime in a resort they had visited.
Mrs May told the House of Commons that the measures would help to tackle cross-border crime. "It does not amount to a loss of sovereignty," she said. "It will not unduly burden the police. It does not incur a loss of civil liberties. It is in the national interest to sign up to it."
She acknowledged that the existing draft EIO was "not perfect" but by opting in at this stage "we have the opportunity to influence its precise outcome".
The decision was welcomed by the shadow Home Secretary, Alan Johnson, but he warned Mrs May that she may face stiffer opposition from her own backbenchers.
The power would allow prosecutors from any European Union country to place people under surveillance, bug telephone conversations, and monitor bank accounts.
Jago Russell, chief executive of the campaign group Fair Trials International (FTI), said: "Police time could be wasted with dealing with unreasonable demands for evidence and the cost to our privacy could be enormous. Police officers from Portugal to Poland would have free rein to demand recordings of our private conversations, copies of our bank statements and even our DNA."
An FTI report found the proposals would make it possible for Spanish police investigating a murder in a nightclub to demand the ID of every British citizen who flew to country in the month the attack took place. It could also demand that UK police search the DNA database to see if any of those identified are on it, and to provide the DNA records of any such person to the Spanish authorities.