The annual rate of decline is 4.4 per cent, the biggest fall since the research company started its monthly survey in 2001.
The average home is now worth £168,500 after falling in price for 10 consecutive months.
This comes as the latest figures from the Land Registry reveal that average house prices in England and Wales fell one per cent in June. This takes the average price to £180,781.
Land registry figures show a decline for the tenth consecutive month, with an increase of 0.1 per cent.
House prices in London fell by 2.5 per cent in June – more than any other region in England and Wales, taking the average London house price to £345,136.
The North East bucked the downward trend being the only region to experience growth, with a monthly increase of 4.1 per cent.
Director of research Richard Donnell says: “Indicators of market activity across the housing market remain weak, with the survey highlighting a 20 per cent drop in demand over the past three months.”
“Transactional volumes have been the greatest casualty of the decline in demand over the last 12 months – the vast majority of homeowners simply do not need to move.”