Prime Minister David Cameron is under pressure from Tory bankbenchers after the coalition suffered a drubbing in local elections
Labour has been celebrating significant gains in council elections across Britain, but failed to win the mayoral race in London, where Boris Johnson's victory provided a consolation prize for Conservatives on a grim day for both coalition parties.
Tory favourite Mr Johnson defeated Labour's Ken Livingstone for the second time in succession, but the winning margin of 51.5% to 48.5% was tighter than predicted in many polls and the result was delayed until minutes before midnight by glitches in the counting process.
Mr Johnson promised to dedicate his second four-year term to "fighting for a good deal for Londoners", while Mr Livingstone announced he had fought his last election.
Congratulating his rival, Mr Livingstone said he suspected that Mr Johnson had now sealed the result of the next Conservative leadership contest.
After counting was completed in all 181 councils holding elections in England, Scotland and Wales, Labour had exceeded expectations by gaining 824 seats and winning control over an additional 32 authorities, while 403 Tories and 330 Liberal Democrats fell victim to a cull of coalition councillors.
A BBC projection put Labour's share of vote at 38%, with Conservatives on 31% and Lib Dems on 16%, but low turnouts averaging less than one-third of eligible voters reflected widespread public disengagement from the political battle.
The results represented Labour's most successful showing in council polls since Tony Blair's leadership, and saw them make deep inroads into constituencies in the Midlands and south of England which Ed Miliband will have to win if he is to stand a chance of entering Downing Street at the general election scheduled for 2015.
Mr Cameron faced demands from a string of Tory right-wingers - including one minister - to rein in his coalition partners, refocus on Conservative priorities and drop "barmy" proposals on gay marriage and reform of the House of Lords.
And senior Lib Dem peer Lord Oakeshott issued a warning to Nick Clegg that his party will no longer be a "nationwide, powerful, independent force" by 2015 unless he takes urgent action to revive its fortunes.
Mr Cameron and Mr Clegg are expected to attempt to relaunch the coalition with a joint press conference on Tuesday, ahead of the May 9 Queen's Speech which will set out the Government's agenda for the coming year.