Treasury Chief Secretary Danny Alexander has made it clear that the Coalition's Help to Buy scheme will not be used to enable middle class Britons to buy second homes.

It came as confusion was sown over the details of the Lib-Con plans, a centrepiece of the Budget, to get more people on to the housing ladder and to get more homes built.

Chancellor George Osborne had initially ducked questions about whether the proposed scheme could be used to help people buy second homes.

Ed Balls, his Labour shadow, said it was a "spare homes subsidy" for the better-off.

Mark Prisk, the Housing Minister, in a bid to clarify matters on second homes, said: "Let's be clear, that is not the case. You would first have to divest your existing property prior to being able to proceed with any Help to Buy sale. This is about family homes; it is not about second homes."

Later, Treasury sources clarified the minister's remarks, suggesting Mr Prisk had only been referring to the "equity loan" element of Help to Buy.

They stressed the UK Government was working out details of the second element of the scheme – the £130 billion mortgage guarantee available to all homebuyers – with the industry before its launch next January.

It was suggested that the issue of second homes was not as straightforward as it at first seemed with the example given of homeowning parents underwriting the mortgage of their child under the Government scheme.

Mr Alexander said: "The purpose of the scheme is about helping those people to get on the housing ladder because of the cost of a deposit. That's what we are aiming at; we're not aiming at supporting the purchase of second homes."