Gordon Brown has hit out at the Tories for playing "fast and loose" with the Union of England and Scotland.
In a series of broadsides at Conservative leader David Cameron - almost certain to be his opponent at the next election - the Chancellor also insisted he would have nothing to do with the "celebrity culture" that "tells people what they want to hear".
He also set out his plans for reconnecting the Government with the public by creating a "servant state" during a question and answer session at the Fabian Society's conference in central London.
Mr Brown said there was an increasing "division" between the Labour Government, who wanted to stress what united England and Scotland, and opposition parties who used controversial issues to score political points.
Such people were playing "fast and loose" with the union and putting its whole future at risk.
He identified one point of strain as the campaign for only English MPs to be able to vote on English laws - which has been supported by Mr Cameron.
The Chancellor was asked by former Labour MP Oona King whether he was concerned that he was seen as too "serious" compared with Mr Cameron.
She said: "You, Gordon Brown, can't match David Cameron for being lightweight and fluffy."
Mr Brown replied: "I'm not going to do something that I'm not simply to get attention.
"I think celebrity in the modern world is just like someone who walks into a room and says 'what do people want to hear and I'll tell them?'."
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