Video: Mansion tax could wipe 5pc off the value of high-end London homes All in all, homes worth over £2m could fall by an average of 5pc if the proposal is adopted. The Labour party leader has come under fire from the property industry over his mansion tax stance amid fears it will make the UK less competitive. "The UK's prime housing market [the top 5pc to 10pc of homes by value] is expected to slow in the run up to next year's election and grow steadily thereafter, but the introduction of a mansion tax would change the outlook dramatically," said Sophie Chick, senior analyst at Savills. It would take some time for the markets to accurately price in the impact of a mansion tax, but the threat has already slowed the market. With the majority of £2m-plus homes residing in London, the findings are heavily weighted towards the capital. In its wider housing market forecast, which accompanied the mansion tax analysis, Savills predicted that after a muted 2015 house price growth will gain momentum. The rate of growth is set to outpace that of the capital over the next five years, with the average UK home seeing a 19.3pc rise in value by 2019. Wage rises, an improving economy and parents passing using their money to help their children get on the property ladder, a trend that is set to continue, should bump up sales from 1.2m this year, well below their pre-crash average of 1.7m, according to Savills. The South East will streak ahead with 26.4pc house price growth over the next five years, followed closely by the East of England (25.2pc), whereas London, which has seen runaway prices, will only achieve 10.4pc in comparison - the slowest of all UK regions. "Mainstream market performance will be limited by buyers' capacity to borrow and service debt, but we don't believe rate rises will be severe enough to trigger a wholesale market correction, so are not forecasting price falls," said Lucian Cook, head of residential research at Savills.