Liberal Democrats have a "duty" not to scupper plans for elected police commissioners even if they are a Conservative-inspired policy, Nick Clegg indicated today.
The Deputy Prime Minister insisted his party would respect its role in the coalition Government after a Lib Dem peer led a revolt which saw the move rejected by the House of Lords.
Baroness Harris said allowing voters to choose commissioners would do "irreparable damage" to the police and 13 party colleagues backed her amendment giving the choice to a local panel instead.
The shock 12-vote defeat in the upper chamber over the flagship law and order legislation marred the anniversary of the formation of the power-sharing administration.
Mr Clegg, who has promised to show more "muscular" Lib Dem influence in the coalition after last week's hammering for the party at the ballot box, said the defeat would be reversed in the Commons.
But, giving evidence to the Commons political and constitutional reform committee, he was keen to stress that the idea was not one which had been promoted by his party.
"It is a coalition agreement commitment and I take very seriously, even in cases which don't, as I say, flow from one side of the coalition, our collective duty to honour what we've said we were going to do in the coalition agreement.
"And that's why the Government will seek to reverse that vote last night."
Mr Clegg had indicated his support for his peers' efforts to slow the introduction of elected commissioners by piloting the scheme - but the upper house went much further.
But one of the Lib Dem peers who abstained in the vote insisted the legislation did not meet the coalition agreement which promised "strict checks and balances" on the new commissioners.
Baroness Hamwee, vice-chair of the Lib Dems' backbench home affairs committee, said: "I hope what has happened is going to allow a rethink which will reflect better the coalition agreement."
"The new model should be subject to 'strict' checks and balances. There was certainly no confidence that what is in the Bill at present amounts to that.
"I hope what has happened is going to allow a rethink which will reflect better the coalition agreement."
Shadow home secretary Yvette Cooper said the Lords had "ripped the heart out" of the legislation.
"David Cameron and (Home Secretary) Theresa May need to now recognise the strength of hostility and ditch the plans now," Ms Cooper said.
The blow last night came just hours after the Prime Minister told his MPs that the alliance with the Lib Dems benefited them because it meant they could push measures through parliament.
Prime Minister David Cameron and Mr Clegg are at a joint event on tackling youth unemployment this afternoon, as they seek to move on from bitter wrangling over the electoral reform referendum.
Both have insisted that the coalition will survive the recent disputes but Mr Cameron told his MPs yesterday the Lib Dems should not be allowed to portray themselves as a "moderating influence".
Under the Police and Social Responsibility Bill, police and crime commissioners (PCCs) were due to be elected from May next year to replace police authorities in England and Wales.
They would have the power to hire and fire chief constables and would set the police force's budget and "strategic direction".
But the amendment states that the commissioners will be chosen by a local police and crime panel.
The result raises the prospect of a major parliamentary battle, with the Government pledging to overturn the change when the Bill returns to the Commons.
A Home Office spokesman said: "The election of police and crime commissioners is a clear Coalition Agreement policy.
"So while we will consider the debate in the Lords, we will look to redress this in the Commons."
Rebel Lord Bradshaw, who speaks for the Lib Dems in the Lords and is former vice-chairman of a police authority, said it would be "extremely difficult" for a party-political commissioner to be seen do an impartial job.
"The coalition agreement said that there should be adequate safeguards and we have seen no evidence of that at all," he told BBC Radio 4's The World at One.
He said he did not care if his opposition got him sacked as a spokesman and would not change his mind on the issue.
Policing minister Nick Herbert said all three main parties had proposed direct accountability for policing in one form or another in their manifestos - and blamed the revolt on former members of police authorities upset about their abolition.
There were "points of detail to discuss" but the legislation did provide all the necessary protections, he said.
Having Tory London Mayor Boris Johnson in a similar role in London had proved popular with people in the capital, he said.
And he dismissed criticisms from former Scotland Yard head Lord Blair - who was forced out as Met Police Commissioner shortly after Mr Johnson took charge of the police authority.
"Of course, as someone who lost his job in London I can understand why he takes a particular view," Mr Herbert said.
He denied the defeat was politically destabilising - pointing to the support of three quarters of Lib Dem peers for the Government position.
The Thatcherite Conservative Way Forward group - which counts Foreign Secretary William Hague among its honorary vice-presidents and argued against the formation of the coalition - urged Mr Cameron to curb the Lib Dems' "undue influence"
Chairman Don Porter said: "We are calling on David Cameron and the Conservative Party leadership to reject the demands for concessions in the same way that the British people have rejected the Liberal Democrats.
"Now is not the time to be turning further to the left, but instead taking the necessary action required to rebuild our country and economy after a decade of Labour mismanagement."
Mr Cameron and Mr Clegg, answering questions alongside each other at the 2012 Olympic park, said it was too early to judge the success of the coalition.
The Prime Minister said the voters would not be swayed by unspecified "fripperies" but by whether the Government delivered "good results about the things that British people care about".
"That's what we're focused on, that's why it's a five-year Government and that's why I believe it will endure," he said.
Mr Clegg told reporters: "Polls go up and down. People's popularity goes up and down, parties' popularity goes up and down.
"At the end of the day, how will we be judged? We will be judged about whether we have sorted out the mess we have inherited and restored a sense of optimism, of prosperity, of jobs for this country. It is a job we have started and we are going to see it through.
"This was always going to be the really, really tough part for the coalition and the tough part for the country economically."Reuse content