Gordon Brown today acknowledged a "bad night" for Labour after the party's national share of the vote plummeted to 24% - its lowest level since the 1960s – in his first electoral test as prime minister.

With about two thirds of the results declared, the Conservatives had 44% of the national share of the vote – enough to give David Cameron a landslide majority if it were replicated in a general election.

The Liberal Democrats, on 25% of the vote, pushed Labour into third place for only the second time in their history.

In what could be a further blow for Brown, Labour and Tory sources were both privately predicting that the Conservative candidate, Boris Johnson, would be elected mayor of London when the results of the mayoral contest are announced this afternoon.

Turnout in London was estimated to be 45%, better than in the previous two mayoral elections in the city.

Brown today promised to listen to the concerns of voters. "This has been a disappointing night, indeed a bad night, for Labour. We have to listen and learn from that and then we will move forward. My job is to listen and to lead and that is what I will do," he said.

In another blow to Brown, Labour announced today that David Pitt-Watson, a banker appointed as the party's new general secretary with strong personal backing from the prime minister, would not now be taking up the post.

Pitt-Watson, who was appointed in March but had not yet taken up his post, was due to replace Peter Watt, who resigned last year after the controversy about Labour accepting proxy donations. Labour said it hoped to find a new general secretary soon.

The prime minister suggested that "difficult economic circumstances" were a factor in Labour's defeat. He insisted that the government was taking steps to help people with their mortgages and their food and fuel bills.

"The test of leadership is not what happens in a period of success but what happens in difficult circumstances. And the challenge is to show that we have the strength and the recognition, as well as the convictions and ideas, to take the country forward. And that is exactly what we are going to do," he said.

With the final results available all 159 councils in England and Wales where there were elections, the Tories were up 256 seats, Labour down 331 and the Liberal Democrats up 34.

The Conservative result was four percentage points higher than in the 2007 local elections. According to the BBC, the 4% increase applied in the north of England as well as the south.

The extent of the Conservative gains would put the party on course for a majority of 138 if they were replicated in a general election, although electoral experts insist this is never an exact guide to what will happen in future.

The Tories said that five cabinet ministers - Jacqui Smith, the home secretary, James Purnell, the work and pensions secretary, Ruth Kelly, the transport secretary, John Denham, the universities secretary, and John Hutton, the business secretary – would lose their seats if people voted the same way in a general election as they did on Thursday.

Under this scenario, the Conservatives would be returned with a landslide and Labour would lose 182 seats. The party would be left with just 169 MPs.

David Cameron, the Conservative leader, who embarked on a victory tour of areas where his party won councils, told the BBC: "This is a very big moment for the Conservative party, but I don't think anyone would think that we would deserve to win an election on the back of a failing government. I want us to prove to people that we can make the changes that they want to see."

Harriet Harman, Labour's deputy leader, said this morning that the results were "very disappointing" for her party.

"People are concerned about food prices and increases in fuel bills and there are worries about financial instability. We have got to really recognise these concerns and do everything we can to protect people from the economic problems that are out there," she said.

The Tories, who have taken control of 12 councils, hailed their performance in the bellwether boroughs of Bury in Greater Manchester and North Tyneside as a sign that the party was breaking through in northern England.

Their gains also included Southampton, a battleground city with Labour in a general election, the Vale of Glamorgan in South Wales, and Harlow, a highly marginal parliamentary seat in Essex held by the higher education minister, Bill Rammell.

Although Labour lost control of Reading, which had been their only council in south-east England, they picked up another one in the region when they took control of Slough.

A Conservative spokesman said: "Gordon Brown has had his Life on Mars moment. He went to sleep in 2008 and today he's waking up with support back to the worst his party has seen since records began in 1973."

The shadow chancellor, George Osborne, claimed it was a "truly shocking night for Labour" as the Conservatives made gains in town halls across the country.

He said: "There's always this argument that the Conservatives can't win in the north. If you look across the north, we are doing extremely well."

But his party failed to clinch Worcester city council in the Midlands.

Labour sources described the result as "a mauling" and admitted that Ken Livingstone is likely to lose the London mayoralty to Boris Johnson, the Conservative challenger, later today. Vincent Cable, the Liberal Democrats' deputy leader, said earlier he believed that Johnson had won.

Were the votes to be replicated in a general election, cabinet ministers John Denham (Southampton Itchen) and James Purnell (Stalybridge and Hyde) would have lost their seats. Denham told the BBC: "We will get over the difficult times we are going through at the moment."

He admitted that voters felt "shaky" about the economic climate, but added: "We will come back from this and win the next general election."

Geoff Hoon, the chief whip, insisted: "There is no crisis."

But Brown is likely to face intense and conflicting pressure to provide a solution to Labour's electoral woes.

Charles Clarke, the Blairite former cabinet minister, said: "We have got to focus on how and when and what we do. This is a real message to us from the electorate saying: 'We don't like some of the things [you] are doing,' and we have got to get our act together. We have to get our message and purpose across in a more convincing way than we have done."

The Lib Dems narrowly clung on to Liverpool city council. The party had 45 out of 90 seats but clinched control when an independent switched allegiances, giving the Lib Dems a majority of one.

A BBC survey conducted by ICM and published on the BBC website suggested that Cameron was seen as the most effective of the main party leaders.

Of 1,005 people who took part, 68% said the Tory leader was an asset to his party, compared with 43% for Clegg and 42% for Gordon Brown.

Councils changing hands by 7.15pm

Conservative gains: Nuneaton and Bedworth (from Labour), West Lindsey (from Liberal Democrats), Redditch, Basingstoke and Deane, Bury, Cardiff, Elmbridge, Harlow, Maidstone, Southampton, Wyre Forest, North Tyneside, Solihull, Rossendale, Vale of Glamorgan (all from no overall control)

Liberal Democrat gains: Kingston-upon-Hull, St Albans, Sheffield and Burnley (from no overall control)

Labour gain: Slough (from no overall control)

No overall control gains: Caerphilly (from Labour), Colchester (from Conservatives), Coventry (from Conservatives), Flintshire (from Labour), Gwynedd (from Plaid Cymru), Hartlepool (from Labour), Pendle (from Lib Dems), Reading (from Labour), Torfaen (from Labour), Wolverhampton (from Labour)

Independent gains: Blaenau Gwent, Merthyr Tydfil (from Labour)