The Tory leader David Cameron today urged Gordon Brown to call a general election in the wake of Labour's disastrous by-election defeat in Glasgow East.

Speaking outside his home in west London this morning, the Tory leader said: "I think the Prime Minister should have his holiday but then I think we need an election.

"I think we need change in this country, and that's how change should come about."

But the Prime Minister brushed aside the call by Mr Cameron for him to go to the country and call a general election.

"I think my task is to get on with the job of taking us through these difficult economic times," he said.

He was equally dismissive of the prospect of a leadership challenge, saying: "I'm getting on with the job".

He said during a visit to the West Midlands: "My full focus is on taking people through these difficult times."

Mr Brown insisted that the Government was addressing public concerns about rising fuel and food prices.

"I know that people look to the Government to take the action that is necessary," he said.

"We are looking at everything we can so that, in what is a global problem, we can in Britain help people through these difficult times," he said.

Mr Cameron said he was pleased the Conservative candidate Davena Rankin went from fourth place to third place and "maintained" the party's share of the vote.

"But what I wonder is whether we can put up with this for another 18 months," he said.

"I think whenever people have had a chance to speak about this Government, whether at the local elections, whether in Crewe, whether in Henley, whether in the London mayor elections and now in Glasgow, they have said 'Look, we think you're failing and we want change'."

Senior Cabinet minister Des Browne admitted the result was "a bad night" for Labour, but he defended Mr Brown.

Defence Secretary and Scottish Secretary Mr Browne said: "Clearly, this has been a bad night for us and we will take it seriously."

Labour candidate Margaret Curran paid the price for a national mood on economic circumstances, he told BBC Radio Scotland's Good Morning Scotland.

"Time and time again, people raised the issue of rising food and fuel prices," he said.

"They are biting hard and I'm afraid there is no easy short-term solution to them."

Labour had "patiently" sought to explain what Mr Brown and the Government was doing to tackle this international issue, said Mr Browne.

"We have the answers - but there are no easy short-term solutions to these issues," he said.

Action being taken included tax cuts in September and the freezing of fuel duty, and Britain's lead in trying to get the international community to boost food production and tackle energy demand.

Attacking the SNP, Mr Browne said: "Fundamentally, we are entitled to ask others who say they are producing an alternative, what are their policies?

"And they are conspicuous by their absence."

Defending the Prime Minister, he said: "Gordon Brown, in my view and the view of the party, is outstandingly the best politician in the country.

"He is a man of known strengths - the country knows his strengths."

He went on: "At the end of the day, when you ask them who is the man to see us through these tough times, they will tell us that.

"That doesn't necessarily mean that in the environment of a by-election they will go and vote for us, because they are sending other messages."

Labour suffered a similar swing in the Hamilton South by-election of 1999.

Asked if he expected to be a likely casualty in a Cabinet reshuffle, Mr Browne said: "I have moved a number of times in government.

"I have been asked by two prime ministers to do a number of jobs in government.

"I see politics as service - I will serve if I am asked to serve, and I'm quite happy to do that."

Mr Browne told BBC Radio 4's Today programme later that the Government's measures on the economy so far were not enough.

Labour MPs across Scotland will be quaking in their boots John Mason

"We do need to listen," he said.

"And we need to do more of the sorts of things that we've been doing to respond to people to make them feel that there is a sense of fairness about the way in which we are dealing with the challenges that they are facing day to day."

He added: "People do not think that the steps we are taking at the moment are adequately responding to the circumstances that they feel.

"We need to build on what we have been doing - and we planned to do that in any event - but we also need to hold our nerve and hold the course on the longer-term issues."

The loss of Labour's third safest seat in Scotland will create new doubts at Westminster over the Prime Minister's future.

The result, if repeated at a general election, would see Mr Brown lose his seat, along with a slew of Cabinet ministers.

The result came in the early hours, after Labour's insistence on a recount led to the SNP's majority being increased by 11 from an initial 354.

Victorious SNP candidate John Mason and his party leader Alex Salmond said they had achieved a "political earthquake" and the tremors would be felt "all the way to Downing Street".

And SNP deputy leader Nicola Sturgeon denied the victory was solely down to an anti-Labour vote.

"There is no doubt that Gordon Brown and Labour are deeply, deeply unpopular," she told Good Morning Scotland.

"There's frustration on the streets of Glasgow East with a Government that is sitting with its fingers in its ears as people are struggling right now."

Ms Sturgeon said the by-election was the first in UK history fought between two governments - Westminster and Holyrood.

She said: "Yes, it was a vote against Gordon Brown, it was a catastrophe for Gordon Brown, but it was also a positive vote for the SNP and our government in Holyrood."

The Govan MSP denied accusations that the SNP had done the electorate a "disservice" by electing an MP based on a battle with the Prime Minister.

"The electorate clearly wanted to send John Mason to Westminster and I've got absolutely no doubt that John Mason will be a very strong voice for the SNP in Glasgow," she said.

"I know the caveats that must be applied to by-elections, but if this kind of swing was replicated in a general election, it would wipe out every Labour MP in Scotland bar one.

"That puts in context the size of this result."

Asked if independence had been a factor in the vote, she said: "Let's not forget that independence was something Labour put centre stage in this by-election. It was on every Labour Party leaflet and the people of Glasgow East were not scared off by that."

International Development Secretary Douglas Alexander insisted Mr Brown should not bear sole responsibility for the disastrous defeat.

He said voters had been expressing "frustration" over the global economic slowdown and issued a plea for unity from mutinous MPs.

"If you want me to say it is a bad result, it is a bad result," he told the BBC. "I don't think it is a night to say it is about one particular individual.

"I would ask them to reflect on the time when I joined the Labour Party, which was 1982, not in the heady heights of New Labour's success, but at a time of repeated and bitter defeats for the Labour Party.

"We learnt a very serious lesson at that point, which is that divided parties lose."

The by-election, in the party's 25th safest seat in the country, was sparked by the resignation of David Marshall on health grounds.

Labour's campaign got off to a rocky start when its first-choice candidate pulled out at the last moment, but Margaret Curran - already a Glasgow MSP - was widely thought to have fought a solid battle.

A series of positive polls had led to growing optimism among senior Labour figures over the past week that the party would scrape through.

But in the event its vote plummeted from 18,775 at the 2005 general election to 10,912.

Turnout was high at 42%, suggesting constituents voted in protest at the Government rather than staying at home.

The Prime Minister and his Cabinet colleagues have repeatedly denied that losing the by-election would force him to quit.

But it is bound to fuel discontent among backbenchers over his poor personal popularity ratings and presentation skills.

The post-mortem will also focus on the 10p tax row, reform of vehicle excise duty, and whether large numbers of Catholic voters in Glasgow East were alienated by controversial measures in the recent Embryology Bill.

According to calculations by the Press Association, Labour would be left with only one MP in Scotland if the result was mirrored at a general election. Mr Brown, Chancellor Alistair Darling, Des Browne and Mr Alexander would all lose their seats.

In his victory speech, Mr Mason said: "Three weeks ago the SNP predicted a political earthquake. This SNP victory is not just a political earthquake, it is off the Richter scale. It is an epic win, and the tremors are being felt all the way to Downing Street."

He added: "Labour MPs across Scotland will be quaking in their boots."

But Mr Salmond insisted he did not believe the Prime Minister would step down in the wake of the defeat.

"I don't think we will see an immediate exit for Gordon Brown from Downing Street," he said. "I think it is more likely he will change policy rather than change himself.

"The policy that needs to be changed is on the economy. We need a plan for recovery, we need a plan to stave off recession."

The Tories leapfrogged the Lib Dems to come third in the seat - although their share of the vote did drop.

Labour's direction, and Mr Brown's leadership, will face further examination later today at the party's policy forum in Warwick.

Difficult questions remain about the future role of the trade unions in party funding and the extent of their influence on policy.

Tomorrow Mr Brown will meet Barack Obama as the US Democratic presidential candidate continues his tour of Europe and the Middle East.

Nigel Griffiths, Labour MP for Edinburgh South, dismissed Mr Cameron's election call.

"I think that is a silly challenge to make", he told BBC Radio Scotland.

Mr Griffiths said that Margaret Curran could have won had Labour had its candidate in place earlier.

He said tactical voting was a key factor.

"I found myself on the doorstep, yesterday and earlier, people reluctant to look me in the eye - saying they were not voting Labour", he said, "They were quite clearly Conservative and Liberal Democrat voters who were voting for the Scottish Nationalists."

Of the lessons of the outcome, he said: "I think we have to make sure we are addressing the problems that people feel, the pain of higher petrol prices, higher food prices - all these events.

"They want to know that the Government has a strategy, if any government can have one, to tackle these events."

"The strategy is number one, for the Prime Minister to continue, as he has done, to lead the countries making representations to Opec to make sure that oil production is increased.

"Secondly, to ensure food production is not subject to the vagaries of the market, but is sustained and ensures food prices do not fluctuate.

"And thirdly we have to make sure that the banks take action to prevent repossessions which have been the result of their mismanagement of mortgages and the economy."

Chancellor Alistair Darling insisted that Mr Brown was still the best man to lead the party.

"I believe that Gordon Brown is the best Prime Minister. He is the best leader of our party. He has a very clear sense of direction where he believes we as a country ought to go," he told BBC Radio 4's The World at One.

Universities Secretary John Denham said that simply changing leader would not solve the concerns that led voters to turn against Labour.

"What I think would not help us at the moment is to have that sort of debate. I don't think chopping and changing leaders addresses those concerns. I think it is a bit of illusion," he told BBC News 24.

"We have got to show that on the things that really matter to people, we are going to deliver the goods."