The 'West Lothian question' is set to cause Labour a growing headache, according to a new report.

It raises the issue of why Scottish MPs should be able to vote on English matters when English MPs have no right to vote on issues that have been devolved to Edinburgh.

As Labour pushes ahead with its third term reform plan for English services, the Constitution Unit has warned that ministers will increasingly rely on the votes of Scots MPs.

The 2005 general election saw Labour’s majority in England reduced from 117 to 43, meaning that a small backbench rebellion will therefore trigger a West Lothian vote.

Monday's study also warns, however, that Conservative proposals for 'English votes on English laws' would be "fundamentally unworkable".

"It would in effect create a separate English parliament within Westminster, and the potential for an elected UK government unable to legislate for England, its largest constituent part," it said.

"This would cause a constitutional crisis far greater than the West Lothian question itself. This is why the policy has been consistently rejected as unworkable since Gladstone first considered it in 1886.

"A more transparent solution would be to explicitly create an English parliament.

"But only 16 per cent of the public support this option, which is in effect what would be introduced by 'English votes on English laws'."

Researchers Meg Russell and Guy Lodge said: "Given the new electoral arithmetic, and controversial reforms in education, health and policing on the way, the West Lothian controversy is very likely to come to the fore in Labour's third term.

"But there are no easy answers to the problem.

"'English votes on English laws' is unworkable, so the British may just have to learn to live with this constitutional anomaly, as they do with many others."