Prices dropped by 0.8% in August alone, the largest monthly fall since March, after a 0.3% decline in July, Nationwide's figures showed.
The Bank of England has raised interest rates 14 times since December 2021 to 5.25%, and financial markets expect another rate increase this month to 5.5%.
However Andrew Wishart, senior property economist at Capital Economics, said he expected house prices had another 5% to fall, taking the total peak-to-trough decline to 10.5%.
"We think the August data marks the start of a significant further drop in house prices," he said, pointing to weakness in the latest Royal Institution of Chartered Surveyors survey, which shows the most widespread price falls since 2009.
The poll showed respondents expected house prices to be unchanged in 2024 and to rise just over 3% in 2025.
Persons:
Alishia, Robert Gardner, Gardner, Andrew Wishart, David Milliken, Sarah Young, Mike Harrison
Organizations:
REUTERS, Nationwide, The Bank of England, BBC, Capital Economics, Royal Institution, Chartered Surveyors, Thomson
Locations:
South London, Britain