David Cameron would win a general election by 54 seats, based on voting patterns in last week’s local elections, according to a study published this weekend.

The study shows that the problems faced by Gordon Brown as he is poised finally to become prime minister are worse than first thought.

Labour took comfort last week from snap assessments suggesting that its vote held up, but the research shows that the party’s performance was weaker than initially believed in the south, while the Tories gained more ground in the north.

Thursday’s voting shares — 40% for the Conservatives and 26% for Labour — would be enough to give Cameron 352 Commons seats, 54 more than all other parties in a general election. The study is by Professors Colin Rallings and Michael Thrasher, directors of Plymouth University’s elections centre.

Figures by Rallings and Thrasher — two of the country’s leading experts whose vote-share model has accurately predicted recent election results — show Labour’s share of the vote, at 26%, remained at last year’s depressed levels, while the Tories, in gaining nearly 900 council seats, advanced from 39% to 40%.

It comes amid concern yesterday from Brown’s allies that a row over Scottish independence could derail the early months of his premiership. Tony Blair is to announce his resignation this week, and the chancellor is expected to take over as prime minister at the beginning of July.

MPs close to the chancellor acknowledged that the Scottish National party’s achievement in winning the largest number of seats at Holyrood was likely to lead to the “nightmare scenario” of friction over the Union dominating the early months of a Brown administration at a time when Blair’s successor wants to rebuild Labour’s dwindling support among the English middle-classes.

“Gordon being diverted by a running clash with Scotland may only serve to emphasise his own Scottishness and could be politically suicidal,” said one MP. While Brown’s allies say he recognises the risks, he believes the Union is too important an issue to set aside.

Blair will bring the curtain down on his 10-year reign this week, triggering the departure of several of his key allies from frontline politics. Because of the cash for honours scandal, he will abandon any plans for a big resignation “lavender list” to put his supporters into the House of Lords.

Brown intends to make a series of speeches in England and Scotland warning that separatism would amount to the “Balkanisation of Britain”.

Yesterday, Alex Salmond, the SNP leader, issued a series of radical demands to Brown, designed to bolster support for independence and threatening to stoke up tension with Westminster.

They include a greater share of North Sea oil revenues for Scotland, more funding to help set up a local income tax and a new levy on lorries carrying Trident nuclear warheads.

Sources close to the chancellor immediately hit back, accusing the SNP leader of “arrogance”. They insisted there would be “no truck” with deals to appease the nationalists. The chancellor’s allies hope that Labour can instead forge a deal with the Liberal Democrats and continue to rule Scotland in partnership with them.

“The SNP may not even be part of the ruling coalition,” said the source. “Given the circumstances of the election and the fact that a clear majority of Scots voted against the SNP, plans for independence should be binned.

“Alex Salmond is hardly in a position to be making demands on anyone. It is the height of arrogance for him to make such demands in this way.”

Sources close to Brown said he would not even contemplate meeting Salmond until the ruling coalition was finalised and the chancellor has taken over as prime minister.

The chancellor is close to Sir Menzies Campbell, the Liberal Democrat leader, and may seek his help by asking him to bring pressure to bear on his party’s Scottish leader Nicol Stephen to rebuff SNP advances and form a

coalition with Labour. Brown is under intense pressure to make an immediate impact as new prime minister. Instead of spreading eye-catching announcements over his first 100 days, he is now said to be focusing on his “first 100 hours” in office.

Blair’s departure from No 10, to be announced officially on Thursday, is expected to mark the end of the careers of some of his longest-serving ministers and aides, who will retreat to make way for the chancellor.

Among those likely to go is Blair’s former flatmate, Lord Falconer, who is said to be ready to leave the cabinet when the prime minister departs.

John Prescott, the deputy prime minister, will also bow out of frontline politics, while Hilary Armstrong, Blair’s former chief whip, is said to be resigned to losing her place in cabinet.

A string of other leading Blairites were in full flight this weekend as they accepted the inevitability of the chancellor taking over the top job.

Downing Street sources have revealed that Charles Clarke, the former home secretary, abandoned his plans to challenge Brown for the leadership following intense pressure from leading Blairites, who persuaded him that the chancellor could not be beaten.

John Hutton, the work and pensions secretary and one of Brown’s fiercest critics, will demonstrate the seismic shift in power today when he publicly offers the chancellor his wholehearted support and calls on the Labour party to throw its weight behind the new leader.

John Reid, the home secretary, who considered challenging Brown for the premiership, will also hit the airwaves today to confirm finally that he will not challenge the chancellor for the top job.

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