Cable plays down Lib Dem proposal to widen mansion tax Vince Cable has played down the idea that buy-to-let investors could be caught in the net of the Liberal Democrats" mansion tax. A mansion tax on homes worth more than £2m has long been a prized policy of the third party as a totemic symbol of its left-leaning credentials. Yet its Tory partners have consistently prevented it being introduced in government since the coalition was formed in 2010. The party deliberately moved the threshold up from £1m to £2m to limit the 1 per cent annual levy to a small number of the most wealthy in areas such as Mayfair and Kensington. But an internal consultation paper being drawn up by officials says there "may be merit" in applying the levy to property portfolios of £2m-plus - and not just single residences. That would catch thousands of buy-to-let investors and people with holiday homes. The policy paper will be presented at the spring Lib Dem conference in March in Brighton. But Mr Cable, the business secretary, emphasised that the idea was not party policy and "probably doesn't make a great deal of sense" because second homes were already subjected to capital gains tax and income tax on rent. The paper also suggests that inspectors could estimate the value of other assets such as jewellery or art in people's homes to measure their total wealth. However Mr Cable told Sky News this was a "wacky" idea, warning that it was "completely impractical and intrusive." One Lib Dem source insisted that the jewellery element of the plan was probably a "non-starter." The papers emerged just days after Labour sought to appropriate the wider mansion tax policy by proposing a similar move as a way to fund the bringing back of the 10p income tax band. Ed Miliband, Labour leader, has threatened to force a vote on a mansion tax in the House of Commons in an attempt to expose coalition splits over the issue. Paul Johnson of the Institute for Fiscal Studies said on Sunday that a mansion tax was "an awful lot of money from a very small amount of people." Under the original Lib Dem proposals it would raise about £2bn a year. Lib Dem MP Tessa Munt - who has helped to draw up the consultation paper - described the move as an "interesting idea" which would be put to members at the forthcoming conference. But Lib Dem Treasury spokesman Stephen Williams said he expected the plans to be "firmly spiked."