The dip has likely been caused by high net worth individuals deciding not to move to the UK, while others are leaving the country, said Prime Location, the property website that commissioned the research.
The top 25 per cent of houses lost an average of £7,000 in the year to September, with the average price for a prime home now just over £450,000. This is the biggest fall since January 2009, when Prime Location started tracking prices.
Seven of the 11 regions covered by the research saw a fall in adjusted average value, while the other four saw a rise.
Homes in London suffered the most dramatic fall, falling 2.4 per cent in the last month alone. The top 25 per cent of homes now cost an average of £1.1m. Welsh homes fell the most in the year, down 5.8 per cent on average to £334,953.
Scotland has proved the most resilient, with prime properties increasing 2.2 per cent in the year.
Prime Location’s research director Andrew Smith said: “This fall in prices at the top end of the market is particularly interesting because the availability of prime stock has also decreased slightly.
“With the rise in the value of sterling, there could be fewer high net worth individuals looking to buy property in the UK from abroad. In addition, the higher income tax level and general economic climate seems to be prompting some wealthier homebuyers to leave the UK and live in countries with more favourable tax regimes.”