In a double whammy for Labour, the analysis shows that the party will have its overall majority cut to the bone and that several wafer-thin marginals will be created in the South, where Tory leader David Cameron’s appeal is thought greatest.

Had the changes been in place at the last election, Labour’s 64-seat victory would have dropped to 44 with several more seats too close to call, The Times has learnt.

It means that a national swing of just1 per cent will be needed at the next election to wipe out Labour’s overall Commons majority.

The boundary changes have been driven by population drift into the suburbs and make a hung Parliament much more likely, according to researchers.

The extra squeeze on Labour seats in the South helps to explain why Gordon Brown, the Chancellor, expected to be Labour leader at the next election, is trying so hard to stress his credentials with English voters.

However, the Tories will still need a swing of 9 or 10 per cent (down from 11 per cent) to win an outright majority, meaning that the parties may have to fight for Liberal Democrat support to be able to govern after the next poll.

Boundary changes take place every eight or nine years and almost every change from the review begun five years ago has now been settled. Writing in MPs’ The House Magazine today, researchers said: “The principal political impact is to make it less likely that Labour can win an overall majority.

“The boundary review heightens the risk to Labour from a relatively small swing of votes that already exists because of the number of highly marginal seats.”

They add: “After the changes, a swing of only just over 1 per cent would destroy the majority, while under unchanged boundaries it would take a 1.8 per cent swing.

“The situation was uncomfortably tight already, and now Labour has the tiniest margin for slippage.”

If the changes had been in place last year, Labour would have had 347 seats instead of 355, the Tories 209 instead of 198 and the Lib Dems 64, up two, according to researchers Lewis Baston and Simon Henig.

Looking at voting patterns ward by ward, they calculate that, of 13 new seats created by the Boundary Commission, 10 would have been Conservative in 2005 compared with one for Labour and two for the Lib Dems. Of nine abolished seats, all in urban areas, six are Labour, two Conservative and one Lib Dem.

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