LONDON - Prime Minister Gordon Brown once promised he'd lead the world out of its economic crisis. Now he's fighting to save his job.

Two months after he brought U.S. President Barack Obama and other world leaders to London to broker a deal to tackle the worldwide downturn, Brown faces the most serious challenge to his leadership since he took office in 2007.

Cabinet ministers have deserted his government. Rank and file legislators are manoeuvring against him. And a scandal over legislators' excessive expenses claims may finally force the 58-year-old Scot out of the prime minister's official residence on Downing Street.

Four ministers have quit his government in two days, pre-empting Brown's planned shakeup of his ministerial team and creating the image of a government in chaos.

The ministers' decision to abandon Brown just as British voters go to the polls in European and local elections Thursday has been seen by many as an attempt to drive him from office. Many legislators believe the Labour party can only revive its fortunes under a new leader.

Labour legislator Barry Sheerman said Brown must act urgently if he is to stem the tide of dissent.

"If the prime minister doesn't realize that, across the party, there is a disillusionment with the way the parliamentary party has been consulted, treated and valued, he is heading for trouble," he said.

Even the left-leaning Guardian newspaper -- traditionally a supporter of Labour -- said Brown's time was over, calling in an editorial for him to be "cut loose."

"It's highly damaging," said political scientist Alan Finlayson, an expert on Labour. "It gives the appearance that the rats are leaving a sinking ship."

Voters are expected to use elections Thursday to rebuke Britain's three major parties -- but Brown's in particular -- by backing smaller parties to protest excessive expense claims.

Public anger has been fuelled by revelations that legislators expensed items ranging from cookies and cushions to horse manure, swimming pool repairs and bogus home loan payments.

About 15 legislators have said they won't run for re-election. And analysts say hundreds more -- perhaps half those in the House of Commons, which has 646 members -- could be ousted in the next national election, which Brown is obliged by law to call by June 2010.

The latest minister to leave Brown's cabinet is Communities Secretary Hazel Blears, who has faced sharp criticism over her expense claims. She announced Wednesday she would quit her post, and suggested Brown's government had lost touch with voters.

"I want to help the Labour party to reconnect with the British people, to remind them that our values are their values, that their hopes and dreams are ours too," Blears said in a statement.

She had previously ridiculed Brown's attempts to use a YouTube video to explain plans to reform the expenses system, an appearance that was widely mocked for Brown's awkward demeanour and random smiles.

Blears has been criticized for making tens of thousands of pounds tax free by selling a home she was using public money to maintain. She has repaid 13,000 pounds. Brown had described her actions as unacceptable, and he had been expected to fire her in a cabinet shakeup Friday or early next week.

Her resignation follows the decisions Tuesday of Home Secretary Jacqui Smith and two junior ministers -- Beverley Hughes, a junior schools minister, and Tom Watson, a minister and longtime aide to Brown -- to quit their government posts.

The futures of finance and transport ministers are also in doubt.

Smith -- who mistakenly expensed two porn movies -- and Blears were expected to be axed, but the resignations have dented Brown's authority and denied him the chance to sack the miscreant ministers.

Britain's opposition parties are urging Brown to call a national election immediately. "His government is collapsing before our eyes," main opposition Conservative leader David Cameron said Wednesday.

The Guardian reported that a group of rank and file Labour legislators were preparing to ask colleagues to back an email petition calling on Brown to step down. The paper reported that rebels have suggested a new leader could be appointed by July 2.