The London-based high net worth brokerage said it believed the proposals were not only grossly unfair but completely impractical.
Liberal Democrat business secretary Vince Cable recently floated the mansion tax idea as a possible replacement for the 50p top rate of tax levied over incomes over £150,000.
Hugh Wade-Jones, director of Enness Private Clients, pointed out a number of complexities that would make any such levy unworkable.
He said: “There are a huge number of potential sticking points for any mansion tax introduction and in our belief it is likely to do more harm than good given the significant amount of cost that will be incurred in setting up such a scheme.
“One such problem is how the government intends to value hundreds of thousands of homes and who is going to do it?
“Not forgetting that anyone owning a property around the threshold will claim to be under the mark and there will be nothing to stop people presenting their home in an undesirable way to reduce its value. We should also remember that value is subjective until a property is sold.”
Wade-Jones added that a large portion of properties that fell into the £2m and over bracket were owned by trust and company structures and therefore questioned how the government intended to establish who was liable for the tax and how they would enforce it for offshore companies which were not subject to UK tax law.
He said: “In addition, how will they gain access to homes that are empty or those owned by foreign owners who only spend a few weeks a year in the property?
“Given that property prices have doubled every decade for more than a generation, taxing those that may have a valuable home but little or no income is quite frankly nonsense.”
Wade-Jones believes that it is extremely unlikely that the mansion tax would be attached to any house price inflation scale.
“In years to come this won’t just affect the wealthy but will in effect be a tax on growing number within the country which is unlikely to be as popular as the current round of wealth bashing appears to be,” said Wade-Jones.
“Ultimately the cost of setting up and maintaining such a levy would be astronomical and in effect it is trying to suppress one of the few positive areas of economic activity currently.”
