Still no relief for Mitchell as police insist he has to go Andrew Mitchell must either resign or David Cameron should sack him, Police Federation leaders said tonight after talks failed to resolve the row over his abuse of a Downing Street protection officer. During the meeting Mr Mitchell refused to tell the union, which represents rank-and-file officers, what he had said during the confrontation last month. Doing so would only start another "firefight," he reportedly said. But his refusal to admit that he had used the word "pleb" led the federation to demand Mr Mitchell's resignation. By continuing to deny using the term he was questioning the word of the officer involved, the union said. Mr Mitchell was reported by police side to have been "tense" and "upset" when challenged as to whether Downing Street PC was lying. Ken Mackaill, chairman of the West Mercia Police Federation, said the Chief Whip had "refused to tell us what he did say" because he did not want to "impugn the integrity" of the police officer and start what Mr Mitchell described as a "firefight." He added: "But unfortunately that's exactly what's happened. We reached an impasse on the integrity issue. Andrew Mitchell's position is untenable. If he won't resign, I don't think Mr Cameron has an option. The meeting came as Labour stepped up its attacks on Mr Mitchell. Yvette Cooper, shadow home secretary, said the time had passed for clarifications and apologies. Labour has previously raised questions over Mr Mitchell's ability to stay in his post, which he gained in last month's reshuffle, but have stopped short of calling for his resignation or for Mr Cameron to sack him. Some suggested their intervention now was actually an attempt to push Mr Cameron into backing him - knowing that if he stays in post he will find it hard to impose party discipline among already truculent backbench Tory MPs. Some senior Cabinet members have suggested that Mr Mitchell's position is untenable because of his role in imposing party discipline. But he is said to be "clinging on" in the hope that the row fades. Ms Cooper said: "This has gone on long enough. Neither the Prime Minister nor the Chief Whip have proved capable of coming clean swiftly and putting this right. David Cameron needs to put an end to this now and remove Andrew Mitchell from his position. Mr Cameron has called for a line to be drawn under the affair following Mr Mitchell's earlier apologies. Senior police figures have also suggested it was time to move on. But rank-and-file officers remain angry that Mr Mitchell continues to dispute the language the officers reported that he used, most controversially calling them "plebs." Last month, police officers wearing T-shirts emblazoned with the slogan "PC Pleb and Proud" protested outside Mr Mitchell's constituency office demanding a full inquiry. Deputy Prime Minister Nick Clegg said Mr Mitchell had to "explain himself" to the Police Federation. He sidestepped questions on BBC Radio 5 Live about whether he gave Mr Mitchell his full backing, but said: "I hear he's talking to the Police Federation today where I have no doubt he and the Police Federation will want to, I hope, clear the air, draw a line under it." Mr Clegg said he had "no idea" what was said between Mr Mitchell and the officer on the gate. There seems to be competing claims about what was and wasn't said. What I do know just from hearing about it is it was really wrong to be rude to a police officer literally just standing there in Downing Street doing his job. I think what he did was wrong, really wrong. He's got to explain himself to the Police Federation, as he is today. Resign or be sacked, demand police Its website boasts that it can "release" your "stress and tension and increase your energy levels," and it is "a wonderful place to relax and unwind." So perhaps it was appropriate that the beleaguered Chief Whip Andrew Mitchell chose to open The Holistic Practice in his Sutton Coldfield constituency today, before his ill-fated showdown with representatives of the Police Federation. Mr Mitchell may want to return after the encounter.