TENSIONS have mounted at the top of the Liberal Democrats after Vince Cable's warning of a housing bubble was slapped down by senior colleagues and the Business Secretary was said to be sympathetic to a rebel amendment in today's key economic debate.

Mr Cable, often regarded as the party's economics guru, has called for a rethink of the Chancellor's Help to Buy scheme, warning the flagship plan to let people buy homes up to £600,000 on a 5% deposit could create an unsustainable boom.

However, both Nick Clegg and Danny Alexander rounded on Mr Cable, flatly rejecting his fears and making clear the scheme would go ahead as planned.

The Help to Buy scheme was the centrepiece of George Osborne's spring Budget and is due to be extended in January to cover more buyers than those just purchasing a new house or flat.

But Mr Cable has said the Coalition should consider changing or cancelling the policy "in light of changing market conditions". Critics have also suggested the scheme could be limited to those parts of the UK where prices are depressed.

Last month, the Secretary of State warned: "We mustn't risk returning to the problems of the last decade when housing got out of control."

But yesterday, the Deputy Prime Minister and Chief Treasury Secretary dismissed their colleague's concerns.

Mr Clegg said Britain was "nowhere near back to an unsustainable housing bubble".

Mr Alexander accepted there were very high house prices in London but stressed: "I don't think we should allow the tail of central London to wag the dog of this policy."

A split at the top of the party emerged ahead of today's major debate on the economy, with two rebel amendments to be debated which seek to "rebalance" the Coalition's fiscal mandate, which the leadership believes is code for moving away from spending cuts towards more tax hikes.

Today in his conference speech Mr Cable will announce a consultation on zero-hours contracts that could lead to a ban. The Low Pay Commission will be asked to examine whether the minimum wage could rise faster, and plans will be unveiled to make company directors more accountable for their actions.