Analysis: Time is Labour's only comfort

A year ago Labour MPs were clamouring for a snap general election - and David Cameron was praying there would not be one.

Today the roles are reversed, with the Conservative leader challenging Gordon Brown to bring on an election after Labour's crushing defeat in the Glasgow East by-election.

There is no chance of that - and the only crumb of comfort for Labour MPs on a grim day is that there are nearly two years to go before the next election must be held.

A Micawberish strategy of hoping something will turn up is a pretty bleak strategy. And things will get worse before they get better, as today's announcement of a further significant hike in domestic gas prices demonstrated.

The loss of such a safe seat - it had been in Labour's hands for almost 60 years - stunned Labour MPs, even though they have become pretty used to hearing bad news in recent months.

Labour has already lost power in London - with Boris Johnson ousting Ken Livingstone as mayor; suffered the humiliation of a lost deposit in the ensuing Henley by-election; seen a healthy Labour majority melt away further north in Crewe and Nantwich; and now received a kicking from the voters in its Scottish heartlands.

It means that no Labour seat is safe at a by-election. Throughout the 1980s, when Margaret Thatcher's Tories turned most of England blue, Scotland remained loyal to Labour.

The Glasgow result is a further sign that old loyalties are breaking down and that the SNP, already in power in the devolved parliament in Edinburgh, is on a roll that could eventually lead to an independent Scotland.

The Tories pushed the Liberal Democrats into fourth place in Glasgow East - a further sign that the Lib Dems are being squeezed as the Conservatives under Mr Cameron re-occupy the centre ground.

The mood among Labour MPs varies from deep gloom to gallows humour. There are reports that some ministers are even taking soundings in the City about the possibility of directorships - a sure sign that they are preparing for alternative employment after an expected election defeat.

Even though Mr Brown today brushed off the threat of a leadership challenge, insisting he was "getting on with the job", some senior Labour figures, including former Cabinet ministers, predict that he will not lead the party into the next election and could be gone by Christmas.

A significant group of Labour backbenchers is ready to move against Mr Brown provided they can find someone senior in the cabinet to wield the dagger. A change of policy is not enough - there needs to be a change of leader, they say.

There is no sign yet of any organised plot against Mr Brown. The by-election was deliberately timed to be held just after MPs had broken up for the long summer break - to minimise opportunities for plotting.

Cabinet ministers, in public at least, are rallying round, even though many now have doubts about Mr Brown's leadership. There is no one yet to fulfil the role of Brutus - the leading lights of the next generation of Labour politicians, David Miliband and Ed Balls, have no wish to be the assassins.

They seem more interested in jockeying for position after the next election, particularly if Labour goes down to defeat. A debate has already begun in Labour think tanks on the "post-Brown era".

And, if there were to be a leadership election later this year, the young pretenders would face a strong challenge from the likes of Jack Straw and Alan Johnson - while refugees from the Blair era, such as Alan Milburn and Charles Clarke, might be tempted to throw their hats in the ring.

Mr Brown cannot afford to relax. There never was any likelihood of a summer plot to depose him, despite the slide in the government's popularity. But dangerous times lie ahead.

If a planned relaunch at the party conference in the autumn, preceded by an expected Cabinet reshuffle, fails to provide an uplift, Mr Brown will come under pressure to stand aside.

Lady Thatcher was unceremoniously dumped by Tory MPs in November 1990 and two years ago Brownite Labour MPs returned from their summer holidays determined that Mr Blair should set a date for standing down.

If the government is still trailing the Tories by 20 points this winter, Labour MPs may start to panic. That would be effectively the last opportunity to remove Mr Brown and instal a new leader whose priority would be limit the scale of Labour's defeat to ensure they were not out of office for a generation

Mr Brown is in no mood to stand aside. He has not waited a decade for his chance to be Prime Minister to be pushed aside by rebellious backbenchers a year after entering No 10.

He is said to accept that he is not connecting with the nation - however hard his army of spin doctors try to get him to sound more human and spout fewer statistics like an "I speak your weight" machine.

Now that the unions are providing almost 90% of Labour's funding, they are planning to flex their muscles at Labour's policy forum in Warwick this weekend. There has already been a wave of public sector strikes over pay - with more planned - and the more militant unions are pressing for more than 100 concessions on issues ranging from an end to privatisations to free school dinners at primary schools.

Mr Brown has already rejected demands for a return to secondary picketing or other concessions that make it easier to strike. After having to abandon the fiscal targets on which he built his reputation for economic prudence as the economy nosedives, Mr Brown will be anxious to show that his government is not at the beck and call of the unions.

There is one thing Mr Brown's friends and foes agree upon. He badly needs a holiday to recharge his batteries after a dismal year in which he has gone from hero to zero.

David Cameron has joined Labour MPs in urging Mr Brown to take a decent break - he ended his holiday after only four hours last year to rush back to London for the foot-and-mouth outbreak. According to Mr Cameron, no-one wants an exhausted and frazzled Prime Minister taking decisions - and even Labour MPs accept that.