If political history is any guide, Gordon Brown is heading for certain defeat in a British general election next year.

Economic and political blows are raining down on the Labour prime minister, eroding his authority by the day and increasing the similarities with the plight of John Major, leader of the Conservative government swept away by Labour in 1997.

Credit ratings agency Standard & Poor's cut its outlook on Britain to negative on Thursday, leading Brown's Conservative opponents to renew their attacks on his economic policies just as the prime minister struggles to contain the damage from a scandal over politicians' expenses.

Labour is polling in the low 20s percent, around 16 points behind the opposition Conservatives who are increasingly confident they can return to power.

I don't think there is any other outcome than a Labour defeat, said Neil Carter, politics professor at York University. At the moment the only thing open to discussion is the size of the Conservative majority.

Comparisons with the situation a year before the end of the Conservatives' 18 years in power back up this point of view.

In local elections in May 1996, 12 months before the general election, Labour polled 43 percent to the Conservatives' 27 -- a 16-point lead but a smaller one than opinion polls were showing.

Major left calling that general election until the last moment and Brown looks certain to repeat this stance in the hope of some form of political redemption -- May 2010 looks the most likely election date.

Labour emerged from the May 1997 election with a 179-seat overall majority after taking 43 percent of the vote to the Conservatives' 31 percent.

Steven Fielding, director of the Center for British Politics at Nottingham University, sees defeat for Brown at the next general election as inevitable but says it will be harder for the Conservatives to achieve an absolute majority.

The battle now is how big a defeat will it be for Labour and whether they can prevent the Conservatives getting an overall majority. That's still a tall order for the Conservatives, he said.

Fielding said that Brown's problems were not as fundamental as Major's. His (Major's) government was fatally divided, in a way this government is not divided, over Europe, he said.

The economy is unlikely to ride to Brown's rescue. S&P said Britain's debt could approach 100 percent of economic output as the Labour government spends billions to bail out the banks and ease the pain of Britain's worst recession since World War Two.

The Brown government's credibility was further weakened when it caved in to public pressure on Thursday and allowed more Nepalese former Gurkha soldiers to settle in Britain.

Brown was forced into a U-turn after suffering his first parliamentary defeat on the issue last month.

HOLDING ON

The scandal over legislators' expenses has hurt all major parties but particularly Labour as they are viewed as having done little to reform the system during 12 years in power.

Justin Fisher, professor of political science at Brunel University, said Brown still had a chance of recovery.

In the past three or four months economic optimism has started to rise. If that rise continues ... that could well be a rewarding outcome for the government. I think that is the thing they will pin their hopes on, he said.

Brown, who took over from Tony Blair as prime minister two years ago after a decade as finance minister, may not get the chance to lead Labour into the next election.

He could face a Labour leadership challenge if the party does particularly badly in June 4 local and European elections, when fringe parties such as the far-right British National Party are set to benefit from voters deserting the main parties in protest at the expenses scandal.

The aftermath of the results in June could be the final opportunity for those who want to get rid of Brown, Fisher said. Health Secretary Alan Johnson has emerged as the media favorite to succeed Brown.

But a poor result may not be terminal for Brown. Labour won just 23 percent of the vote in a 2004 European parliament poll but still won the general election a year later.

SHUFFLING THE PACK

The Conservatives, who want action to restrain the ballooning national debt, seized on the S&P report to renew their calls for an early general election.

UBS economist Amit Kara said the key message for the government was that at some point in the not too distant future they will have to slash spending and consolidate the fiscal position quite dramatically.

Brown's reputation for economic competence and fiscal prudence, built up over a decade of prosperity, has been shattered by the recession.

Opponents mock his oft-repeated pledge to have ended boom and bust although he has gained credit for helping to lead the international response to the financial crisis.

Business leaders have attacked Brown for breaking an election manifesto pledge and planning to raise the top rate of income tax to 50 percent to try to narrow the budget deficit.

Brown is expected to try to shore up his government after the June 4 election by shuffling the cabinet. Local Government Secretary Hazel Blears, who has been caught up in the expenses' controversy, could be a casualty.

The Financial Times said on Thursday that Business Secretary Peter Mandelson could be promoted to foreign secretary, replacing David Miliband, once seen as a rival to Brown.