David Cameron's former tutor has warned the Prime Minister's plans to restrict Scottish MPs voting rights as misguided and unworkable.
Vernon Bogdanor, who also taught Nick Clegg politics, suggested that the move would make governing the UK almost impossible.
And he questioned how many laws were really 'England only'.
The Prime Minister was accused of betrayal when he announced plans for 'English votes for English laws' just hours after the independence referendum result earlier this year.
Critics claimed that the Tory leader had waited until millions of votes were cast before setting out his plans.
The Conservatives claim the current system is unfair because Scottish MPs can vote on health and education issues in England that do not affect their constituents north of the border.
They point to votes in the early part of the last decade when Scottish MPs helped to raise the tuition fees paid by students in England.
But Prof Bogdanor suggested that few issues were really 'England only'.
He said: "Any variation in spending on an English matter has a knock on effect on Scotland, since the money allocated north of the border is calculated as a fraction of English spending".
He added: "So, if spending on education in England is reduced, less money is available for the Scottish Government."
He added that he was surprised that Mr Cameron backed English votes for English laws - a policy also supported by the SNP.
"The SNP is separatist; its aim is to detach Scotland from the rest of the UK. It is odd for the Conservatives to support a similar solution," he said.
Mr Cameron's plan was "incoherent" and "incompatible with cabinet government"- a system which requires every minister not only supports government policy but also vote in favour of it.
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