Rightmove fears that rumoured property taxes, which could disproportionately affect the South of England, could further weigh down on a market that is already underperforming the rest of the country.

The average price of property coming to the market for sale rose by 0.4% (or £1,517) this month to £370,257. Annually, however, this represents a 0.1% dip, according to the property portal's latest house price index.

This slight fall is being driven by London and the South, where the number of homes up for sale is up 9% on 2024, a decade high, compared to 2% elsewhere in the country. It also takes an average of five days longer to find a buyer than in the North and Wales.

In the South West, prices are down by 1.3% compared with last year, while in the North West, they're up by 3.2%.

An uptick in new seller asking prices is expected in September, when the traditional back-to-school season boosts activity heading into autumn.

Last month, reports surfaced that the Chancellor was considering replacing stamp duty with a property tax on homes worth £500,000.

In London, 59% of agreed property sales so far this year have been over £500,000 and would be subject to the speculated new tax replacing stamp duty, versus an average of 22% outside London, according to Rightmove's data. In the North East, it is 8%.

Furthermore, more than one in 10 homes (11%) in London are priced at £1.5m or more and would be subject to the rumoured mansion tax, versus an average of just 2% outside the capital.

The market has until 26 November, the confirmed date of the Autumn Budget, to find out if the rumours are true.

Colleen Babcock, property expert at Rightmove, said: "Rumours of property tax changes began swirling in mid-August, and with the Budget itself not arriving until the end of November, this kind of extended uncertainty can affect market activity, especially in the higher price brackets.

"Movers want to be confident in planning their moving costs. Our real-time data has not yet picked up any major shifts, however it's understandable that those who could be negatively affected by the rumoured changes might be in the process of reassessing their short- and medium-term plans. Our analysis highlights how London and South England-centric the changes would be, and these are the areas that are already performing less strongly."