Ministers have accused the Conservatives of threatening the United Kingdom's future with plans to strip Scottish MPs of the right to vote at Westminster on English legislation.
David Cameron, the Tory leader, is sympathetic to the proposal to allow only English MPs to debate issues such as schools, hospitals and prisons that only apply south of the border.
Amid signs of an upsurge in English nationalism, the party said the move would tackle the perceived constitutional imbalance that has grown up since devolution to Scotland and Wales nearly a decade ago.
But Harriet Harman, the Labour deputy leader, claimed that their "very dangerous line of argument" would jeopardise the future of the Union.
"I don't think it is right to break up the United Kingdom and I think that that's where ultimately the suggestion of the Conservatives would go," she told BBC1's Andrew Marr show yesterday.
"We can't have a situation where people are elected as members of Parliament, sent to Westminster, but some of them can't speak on some issues and can't vote on some issues."
Under the Tory plan, a new English Grand Committee, open only to English MPs, would be established to deal with issues that solely apply in England.
MPs from England, Scotland, Wales and Northern Ireland would continue to sit together in the Commons to vote on UK-wide matters, such as taxation, foreign policy and defence.
The plan is the brainchild of the former Scottish secretary and Conservative cabinet member Sir Malcolm Rifkind, and could form the centrepiece of Tory proposals for constitutional reform after the next election.
He denied his proposals would undermine the UK's stability by creating a two-tier system within Westminster. "It would actually strengthen the Union because there is unfinished business," he told ITV1's Sunday Edition.
Sir Malcolm, now the MP for Kensington & Chelsea, said such a move would not stop a Scot, such as Gordon Brown, from being prime minister. But he said it would be unwise to have a minister from outside England in charge of purely English portfolios.
Caroline Spelman, the Conservative Party's chairman, welcomed the proposals, which she said would "complete the devolutionary process".
She said: "Having English MPs voting on laws that only pertain in England would address that sense of unfairness that English MPs had when the Labour government only got its way on tuition fees and foundation hospitals because Scottish MPs were able to vote on that, even though those laws would not apply in Scotland." Ruth Kelly, the Transport Secretary, hit back: "[The proposal] is a recognition by the Conservatives that they are effectively now an English party.
"I don't think they see any prospect of building back their base in Scotland."
Alex Salmond, the leader of the Scottish National Party and the First Minister of Scotland, said that the Conservatives' plan did not go far enough. He said the solution was to have separate parliaments in Edinburgh and London rather than "some sort of spatchcocked solution to appeal for votes in Middle England".
He added that Scottish independence had growing support in England.
Later, addressing his party's annual conference, Mr Salmond stepped up his campaign for a referendum on leaving the UK.
He argued that Scotland would be "immeasurably better off "if it took full control of its affairs", releasing figures which showed it would move from 10th to third in the European league of prosperity.
He said that the SNP would table a Bill in the Scottish Parliament calling for a referendum on independence within the lifetime of the parliament.
He challenged the anti-independence parties, which between them have a majority of seats in the parliament, to try to agree an alternative proposal to the voters.
"If not then do not try to prevent the people from having their say because it is the same people who will decide the next government in Scotland," he told the conference in Aviemore.
The Scottish Parliament and The Welsh Assembly have power over:
Health and social work, education and training, local government and housing, justice and police, agriculture, forestry and fisheries, the environment, tourism, sport and heritage, economic development and internal transport. (The Scottish Parliament has the ability to alter income tax in Scotland by up to 3p in the pound.)
Dealt with by Westminster:
The constitution, foreign affairs, defence, international development, the civil service, financial and economic matters, national security, immigration and nationality, misuse of drugs, trade and industry, various aspects of energy regulation (eg, electricity; coal, oil and gas; nuclear energy), aspects of transport (eg, regulation of air services, rail and international shipping), social security, employment, abortion, genetics, surrogacy, medicines, broadcasting, equal opportunities.Reuse content