LONDON (Reuters) - Asking prices for British residential property slipped slightly more than usual after last month's vote to leave the European Union, though the overall impact remains hard to judge, figures from property website Rightmove showed on Monday.

Average prices for property advertised in the four weeks to July 9 were 0.9 percent lower than in June, a slightly bigger fall than the 0.4 percent drop typically recorded that month as demand softens in the run-up to summer holidays, Rightmove said.

"Perhaps unsurprisingly this July's fall is marginally larger, as political turbulence has a track record of unsettling sentiment," said Rightmove director Miles Shipside.

Compared with a year earlier, prices were up 4.5 percent, slowing from a 5.5 percent rise in June, Rightmove said. The website is used by most British estate agents, and Rightmove says it includes 90 percent of homes for sale.

Rightmove said buyer demand in the two weeks after the referendum was consistent with 2014 levels, but showed a 16 percent fall from 2015. Sales in June 2015 were boosted by a boom after the Conservative Party won an unexpected outright election victory in May 2015.

Other recent data has painted a much more somber picture. On Thursday, the Royal Institution of Chartered Surveyors said uncertainty fueled by the Brexit vote had prompted a "marked drop" in housing market activity, causing buyer interest and expectations of future sales to wither at the fastest pace in years.

Britain's decision to exit the European Union has sent jitters through global financial markets, triggered political chaos in Britain and sent sterling to a 31-year low.

The Bank of England said on Thursday it had revised down its forecasts for British house prices, and most policymakers expected to loosen policy next month, raising the possibility of even lower mortgage rates.

(Reporting by Karin Strohecker; Editing by Andrew Heavens)