Cameron 'playing politics' on control orders - Ed Balls
Labour has accused the government of "playing politics" with national security over control orders.
Prime Minister David Cameron said the controversial anti-terror measures "haven't been a success".
But Labour claims plans to modify them are motivated by a desire to please the Lib Dems, who promised to do so in their election manifesto.
Labour's Ed Balls said Mr Cameron and Lib Dem leader Nick Clegg should put national security first.
The shadow home secretary insisted he would wait until the outcome of a review into control orders, a form of house arrest introduced by the previous Labour government in 2005, before passing judgement on whether they should be scrapped.
But he accused Mr Clegg of keeping up a "running commentary" in the press, amid stories claiming the orders were going to be axed.
He told BBC Radio 4's The World at One: "The experts I have spoken to in the security services and the police are very unconvinced that it is possible to keep our country safe without some kind of successor regime in place. That is not consistent with the Lib Dem manifesto. That is Nick Clegg's political problem.
"And this desperate attempt to play politics with this issue is, in my view, very mistaken."
Mr Clegg is under pressure to prove that he is delivering on Lib Dem manifesto commitments as his party's opinion poll rating hits a new low - but Mr Cameron has insisted control orders are not a party political issue and he would act in the public interest.
On a visit to Leicester on Wednesday, Mr Cameron told the BBC: "I think we need a system that keeps the country safe but that respects our freedoms. Nick Clegg and I are working very hard to bring this about."
He added: "The control order system is imperfect. Everybody knows that. There have been people who've absconded from control orders. It hasn't been a success. We need a proper replacement and I'm confident we'll agree one."
Mr Cameron also said: "It's not about a victory for the Conservatives or the Liberal Democrats. It's about trying to do the right thing for our country, for the security of our country and our civil liberties."
Opponents of control orders say they infringe civil liberties, but supporters, including backbench Tory MPs, argue they are necessary to protect the public.
The BBC understands that discussions have now reached detailed negotiation about the powers that should be put in place instead of control orders. They include curfews, relocation requirements, electronic tagging, travel bans, restrictions on the use of telephones and computers and on who the suspect can meet and where they can go.
The Lib Dem manifesto promised to scrap control orders which lead to house arrest.
A review of control orders was announced in July and is being overseen by former director of public prosecutions Lord Macdonald.
The results had been due to be published before Christmas, but this was delayed amid reports of policy disagreements between the coalition government partners.
BBC home affairs correspondent Danny Shaw said there were currently only eight control orders in force and a few of those were believed to involve "very light touch" measures.
The previous Labour government argued it had to control some suspects who could not be prosecuted because secret intelligence was not allowed in British trials.