The Boundary Commission will recommend new constituencies in counties such as Hampshire, Norfolk and Wiltshire while abolishing seats in areas such as Birmingham, Sheffield and Manchester. The changes will come into force before the next general election.

The Conservatives have complained that the current map is biased in Labour’s favour because it fails to take account of declining inner-city populations and the increased number of people living in suburban or rural areas.

The average size of the electorate in Labour seats is 65,000, compared with 73,000 for Conservative constituencies — an unequal division of voters thought to be worth at least 30 Members in the House of Commons. The overall result would notionally cut Labour’s 67-seat Commons majority to around 50.

A similar shake-up in Scotland is thought to have cost Labour at least ten seats in the general election this month when its majority was slashed by almost 100. Although Tony Blair insists that the Government has sufficient strength left in Parliament to force through its programme, a hard core of backbench rebels are threatening to wreck controversial legislation on incapacity benefits. Other Bills may also be threatened.

At the next election Labour is bracing itself for a tight contest in which it will be defending dozens of “super-marginals” where victories were often wafer-thin. In the last review ten years ago, Labour officials — led by the legendary elections expert, “Mystic Greg” Cook — were commonly accepted to have run rings around their Tory counterparts. But this time Mr Cook has faced stiffer opposition from Roger Pratt, the Conservative representative at dozens of public inquiries where seats are sliced up and thousands of voters shifted from one area to another. Mr Pratt is understood to have persuaded Tory MPs to work with each other rather than seeking to fatten their own majorities at the expense of marginals.

The inner-city seats likely to be subsumed into other constituencies include Birmingham Sparkbrook & Small Heath and Sheffield Hillsborough, as well as one of the Greater Manchester seats of Salford, Eccles and Worsley.

Another facing the axe is Tyne Bridge, where the electorate is just 53,500. David Clelland, who held it for Labour with a 10,390 majority this month, said: “It’s true: we’re being divided up. There are 13 Labour MPs here at the moment but there will only be 12 seats at the next election. The party will have to decide who should be the candidates — I’m not at all concerned about it.” But other Labour MPs are worried. Ed Balls, who has just been elected in Normanton, West Yorkshire, knows that the commission wants to merge his seat with its neighbours including Pontefract & Castleford — where the MP happens to be his wife, Yvette Cooper. Both of them are short-odds favourites for a seat in a Cabinet chosen by Mr Brown before the next election, but less sure they will still have a seat in the Commons.

Another problem may be created in Merseyside where Angela Eagle’s seat in Wallasey is being lined up for a merger with seats across the river. Those affected could include her twin sister, Maria Eagle, the MP for Liverpool Garston.

Although Labour has launched protests against the commission’s proposed changes in Merseyside and West Yorkshire, most of the review is almost complete and will be laid before Parliament for final approval next year. This will recommend new constituencies in Avon, Cornwall, Derbyshire, Devon, Essex, Hampshire, Lancashire, Norfolk, Northamptonshire, Warwickshire and Wiltshire. Labour accepts that at least nine of these are likely to be safe Conservative seats — as will a new constituency being created in the western end of Central London.

But Mr Cook believes some of the “knock-on effects” could firm up Labour majorities in some seats or help the party win back others. A proposed new constituency in Kenilworth, for instance, is likely to take some Tory-voting villages out of the Labour-held Warwick & Leamington constituency, as well as making a revised Rugby seat easier to regain.

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