Labour's mansion tax is going to be a key deciding factor in many of London's marginal constituencies and could cost them up to 10 seats in the General Election.
There are eight marginals in the capital with less than 4,000 votes separating Labour and the Conservatives in which house prices are already around the £2m tax threshold - and a further two seats which could also swing to the Tories.
In these constituencies the prospect of an extra £3,000 house tax a year will have a strong impact on floating voters.
The five seats that could fall to the Tories are - Hampstead and Kilburn, Westminster North, Hammersmith, Islington South and Finsbury, Surbiton and Kingston, and there are five further marginal seats that the Conservatives are likely to hold - Hendon, Brentworth and Isleworth, Enfield North, Ealing Central and Acton, and Battersea.
On top of that there could be some surprises in Labour strongholds like Dulwich and West Norwood, Greenwich and Woolwich, Holborn and St Pancras, and maybe even Hackney South and Shoreditch.
This policy more than any other is going to tip the balance against Labour in the capital.
Tens of thousands of London families will be hit by the mansion tax, many of them have lived in their communities for decades, they are not filthy rich and their "mansions" are often 3-4 bed terrace houses. Several of these middle income families (and the vast majority are) will face a 30% increase in household taxation under Labour, just because their neighbourhood did well in the property boom.
These asset rich/cash poor London families have picked up the equivalent of a Saturday night lottery win in the past 15 years, but as it's all held in bricks and mortar it's not one they can spend unless they leave London.
Labour traditionally did well in the capital in the past but it appears that the party leadership are prepared to sacrifice their London voters in order to find favour north of the border, which is inevitably where these tax pounds are headed. I can't imagine Labour's prospective MPs in London being too happy with this policy and in several marginal seats homeowners will be looking to change long-held Labour allegiances in order to avoid a tax bill they can ill afford.
In the end it may be the Labour party that pays the highest price for this tax on London, with a major shift in the political landscape in the capital from red to blue.
Sayed Bukhari is the CEO of London property development company HPM DevelopmentsSuggest a correction