The largest ever poll of UK marginal constituencies has suggested that the next general election will bring an overwhelming defeat for the government, sweeping the Conservatives to power with a large majority and almost wiping the electoral map of Labour in southern England.

The PoliticsHome.com electoral index, an influential online tracker of British political developments, adds further weight to the consensus that whenever the next national vote is, it will bring David Cameron’s Tories to power.

The index, edited by political journalist and commentator Andrew Rawnsley, predicts that “if a general election were held now, Labour would suffer a catastrophic defeat on a par with that of the Conservatives in 1997.”

A projected Conservative tally of 398 Westminster seats against 160 for Labour and 44 for the Liberal Democrats would leave Mr Cameron’s party with a majority of 146.

The poll shows Labour retreating into its pre-1997 heartlands in the northeast and the Welsh valleys. Apart from a few pockets in London and other major regional cities, the PoliticsHome political map for the south of England is devoid of Labour support.

Eight Cabinet ministers, including the Justice Secretary Jack Straw and Home Secretary Jacqui Smith, would lose their seats if the projections, which surveyed over 34,000 voters in 238 marginal seats, prove to be accurate.

Predicting a swing from Labour to the Conservatives as high as 16 per cent in some regional break-downs, the study presents a dramatically altered political map in the wake of the next general election, which must be held by May 2010.

Data collected indicates that Labour would lose every single marginal constituency it currently holds except two seats in Cumbria, with a total loss of 124 MPs.

However, extrapolating the trend of the swing towards the Conservatives suggests an even greater collapse, with Labour losing 183 seats nationally.

The poll also suggests major gains for the Scottish National Party, which is projected to benefit from Labour’s unpopularity in Scotland.

In what may turn out to be the biggest shift in Scottish political history since devolution, the SNP would become the largest Westminster party north of the border, increasing their UK representation by 17 seats, mostly at the expense of Labour.

While predicting disaster for the Labour Party, the poll suggests that the Conservative electoral juggernaut would be nearly as damaging for the Liberal Democrats, whose Westminster representation could drop by as much as a third.

A swing towards the Tories, predominantly in the West Country, as well as pressure from the SNP in Scotland, is predicted to cut Lib Dem seats in Parliament to just 44.

High profile casualties for Britain’s third party would include home affairs spokesman and former leadership contender Chris Huhne, MP for Eastleigh.

The poll does offer a crumb of comfort for Lib Dem leader Nick Clegg, who has publicly declared his party’s aim to increase its representation to 100 MPs at the next election – Liberal Democrat MPs are judged to be comprehensively the most popular with their constituents.

When asked if they felt their local Member of Parliament was experienced, approachable, independent and influential, respondents in Liberal Democrat constituences were most likely to respond in the positive in all categories.

However, the party has major shortcomings to overcome in its national popularity, with only eight per cent of all respondents stating that Nick Clegg would make the best Prime Minister – a figure which only increases to 28 per cent when considering just Lib Dem voters, marginally ahead of David Cameron on 24 per cent.

Welsh nationalists Plaid Cymru are also set to capitalise on disatisfaction with the current leadership, quadrupling their Westminster representation from one seat to four.

Given the electoral cataclysm which the poll’s data makes extremely probable, Labour officials will likely take little heart from the news that in the London riding of Bethnal Green & Bow, Respect founder and Celebrity Big Brother contestant George Galloway MP is predicted to lose his seat back to the party from which he claimed it amidst a flurry of press coverage in 2005.

The PoliticsHome study appears a few weeks after a similar poll of marginal Westminster constituencies conducted by Channel 4 News, which also predicted a crushing defeat for Labour, with the added detail that most voters would not be swayed to vote for the government by a change of party leader.