Rural property managers, estate agents, and surveyors claim a proposed "mansion tax" is "fraught with anomalies" and would cap luxury Westcountry properties at £2 million.

The controversial levy on high-value homes is favoured by Liberal Democrat members of the Coalition Government, who are pressing for a 1 per cent tax to be included in the March budget. But Conservative Ministers, including the Prime Minister, are against taxes on wealth and plan to reverse the 50p top rate of income tax introduced by the Labour government in 2010.

Rural surveyors and land agents Smith Gore say the measure will not put off top-end buyers in the market for the UK's estimated 80,000 "mansions" but will be an "irritation". Simon Derby, a partner in the firm's Taunton office, said an extra £10,000 to £15,000 per annum is "manageable".

He added: "Where it will certainly have an impact is on those properties that should sell for just over the £2 million threshold, effectively putting a cap on values at £1,999,999."

Rural advisors Saffery Champness said any proposal must be clear and needed to distinguish between luxury city homes and large country estates.

Mike Harrison, a partner in the company's landed estates and rural business group, said: "Until there is a physical proposal on the table rather than just kite flying we won't know for sure how to deal with this.

"However, there will have to be clear distinctions between high-value residential properties in cities and towns and, for example, the small country estate where the house itself may be of relatively low value in the context of the overall property.

"Moreover, that property will invariably be run as part of a business rather than simply as a private residence."

Deputy Prime Minister Nick Clegg has hinted that any battle to include the measure may be fought over future budgets rather than the spending plan next month.

Lib Dem Business Secretary Vince Cable originally proposed the tax while in opposition and insists it is still "very much on the agenda".