A hung Parliament is more likely after the next general election because of changes to the boundaries of MPs' seats, suggests new research.
Boundary changes could have a big impact on the next election result
The Boundary Commission wants changes to most constituencies in England.
Election experts Lewis Baston and Simon Henig say the changes make it less likely that Labour can win an overall majority at the next polls.
But they say it will make little difference to the Tories' chances of winning an outright majority.
The boundaries of Scottish constituencies were changed at the last election to ensure they were all similar sizes.
Now it is England's turn, with recommendations being made to the government in October. Parliament will vote on the proposals before they come into force - probably in time for the next election.
Their recommendations would increase the number of seats in England from 529 to 533, but almost all existing constituencies would be changed and some abolished.
HOW THE 2005 ELECTION MIGHT HAVE LOOKED
Liberal Democrats: 64
Labour majority cut from 64 to 44
Source: Baston/Henig research on possible effect of boundary changes on 2005 election result
In an article for The House Magazine, Mr Baston and Mr Henig say the boundary changes might have cut Labour's majority from 64 to 44 if they had been in force at the last election.
"The principal political impact is to make it less likely that Labour can win an overall majority," they say.
"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.
"After the changes, a swing of only just over 1% would destroy the majority, while under unchanged boundaries it would take a 1.8% swing.
"The situation was uncomfortably tight already, and now Labour has the tiniest margin for slippage."
But the two academics say the electoral system will still be "heavily biased" against the Conservatives.
Even after the boundary changes the Tories would still need a 9% or 10% swing to get an overall majority - rather than the 11% swing they need under the current rules.
The research suggests the new-look seats which would have gone from Labour to Tory if the changes had come into force in 2005 include: Enfield North, Selby and Ainsty, Sittingbourne and Sheppey, Somerset North East and Staffordshire Moorlands.
Other seats would have swung from Tory to Labour, the research suggests, including: Northampton South, Lancaster and Fleetwood and Rugby.