The tax will hit over 82,000 households, costing an average of £14,500 per home, generating £1.2bn in tax revenue per year.
Over two thirds of mansion tax receipts for the whole of the UK would be generated from the three London boroughs, with more than a third coming from Kensington and Chelsea alone.
Lawrence Hall of Zoopla.co.uk, said: “Not only have the Lib Dems and Labour overestimated the amount the proposed tax would generate; up to £2bn estimated versus actually under £1.2bn, and underestimated the number of homeowners that would be affected; 70,000 estimated versus over 82,000 currently and growing daily.
“But it’s also hugely misrepresentative to call it a ‘mansion tax’ when most of the burden will fall on relatively modest family homes and flats in London.”
From the capital alone £1.04bn would be generated, accounting to 87.4% of the whole of the UK, while the rest of the South East would contribute 7.9%.
Only 4.7% of the rest of the UK would be liable to pay Mansion Tax.
Hall added: “Homeowners in London and the South East already pay the lion’s share of UK property taxes with the stamp duty thresholds placing a heavy burden already on higher priced properties.
“Implementing an additional charge based on higher property values over an arbitrary threshold would only serve to further distort the market.”