Brown warns that Cameron 'may have lit fuse that blows Union apart'
Former Prime Minister Gordon Brown has warned David Cameron that he could have "lit the fuse which ultimately blows the Union apart".
Mr Brown condemned Conservative plans for English votes for English laws.
He accused the prime minister of throwing away the result of last year's Scottish independence referendum.
Mr Brown told a House of Commons debate the plan created two classes of MPs, which had never proved successful anywhere in the world.
In what could be his final Commons address, he said there is a myth the Union can survive "this new polarisation between Scotland and England".
Mr Brown added: "The myth is that it is held together by bonds that are so longstanding they can overcome what is seen as a little local difficulty.
"But what may have been true in the aftermath of the Second World War and its shared sacrifice has given way to a new world where none of our ancient institutions are strong enough and popular enough on their own to hold us together.
"The Union cannot survive on mutual respect alone - although it is in short supply at the moment. It will not survive just on the basis of mutual toleration of each other, a minimalist policy of holding each other at a distance for fear we will fight each other.
"The Union will only hold together if there are things the people of our four nations believe they have in common. Only if we emphasise there are common needs and mutual interests and similar values that make us want to cooperate."
Scottish Secretary Alistair Carmichael said there would be no easy answer or quick fix to the question.
To rush ahead would risk creating new anomalies to replace the existing ones, he said, and put pressure on the "hinges of the UK".
The Liberal Democrat minister said the "logical and lasting solution" would be the creation of a federal UK.
But he accepted that could still be a long way off and called for a constitutional convention to try to build a consensus.