Sales of homes worth more than £1 million have plunged by nearly a fifth year-on-year, Land Registry figures show.
Across England and Wales, 851 homes were sold for over £1 million in January, a 19% fall compared with January last year, when 1,049 properties in this bracket were snapped up.
The bulk of transactions involving homes worth more than £1 million were in London, which saw a sharp 23% decline in sales in this bracket compared with a year earlier.
Some recent reports have suggested that political uncertainty, with the possibility of a mansion tax, and affordability pressures have been taking some of the steam out of the property markets in London's most expensive boroughs.
Stamp duty changes in December have made the tax more expensive for some buyers purchasing high-end homes. While the tax has become cheaper for the majority of buyers liable to pay it, the tipping point comes when homes are worth more than £937,500.
The Land Registry's figures show that house prices in Kensington and Chelsea, where the average property is worth £1.29 million, have shown the slowest annual growth over the last year of all the London boroughs, recording a 5.2% upswing.
Westminster was the only other London borough to see year-on-year price growth below 10%, with a 9.9% increase taking the average value to £999,687.
By contrast, Newham, where the average home has a value of £291,364, saw the highest growth of the London boroughs, recording a 19.8% increase.
Matthew Pointon, a property economist at Capital Economics, said: "Uncertainty regarding the mansion tax has taken its toll on prices in prime central London."
Across all price brackets, the number of completed house sales in England and Wales in January stood at 53,168, an 18% fall compared with 65,175 in January last year.
Property values increased across England and Wales by 5.3% over the year to March to reach £178,007 on average and on a month-on-month basis they dipped slightly, by 0.8%, the Land Registry said.
Semi-detached homes have recorded the strongest price growth over the past year, adding 6.1% to their value. A typical semi-detached home is now worth £169,194.
At a regional level, London continues to record the strongest year-on-year price growth, with a 11.3% increase taking the average house price in the capital to £462,799 in March.
The North East was the only region where average house prices were lower than a year ago, with a 2.9% fall taking the figure to £97,444. In Wales, prices recorded a 2.7% year-on-year increase to reach £117,828.
The figures were released as estate agents across the UK reported a lull in the market as house hunters await the outcome of the General Election, with the first-time buyer market in particular seeing a dip.
Less than one in four homes sold in March went to first-time buyers, according to the National Association of Estate Agents (NAEA). Its figures showed that 22% of house sales in March involved people taking their first step on the property ladder, down from 30% in February.
Overall, the NAEA said that demand for property is the lowest in a year. An average of 343 house hunters were registered per branch in March, down from 366 in February.
Nearly two-thirds (63%) of estate agents reported a slowdown in the market as the election approaches, the NAEA said.
The NAEA said the supply of homes on the market has edged up to an average of 48 per estate agency branch, compared with 43 in February.
Mark Hayward, managing director of the NAEA, said: "We may have seen a slight increase in supply this month, but it is not an ongoing trend or a big enough jump to fill the gap for demand.
"Although our agents have seen the market cooling off ahead of the General Election, it will inevitably bounce back again at a rapid rate after May 7, so it is more important than ever that the party elected focuses on increasing the supply of homes."
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