Some 48 percent of postcodes in the country outside of London saw property price gains in April – the highest coverage of price rises seen since June 2004, and three time higher than the level seen a year ago.
Demand still outstrips supply and nationally the time houses spend on the market has fallen to 6.3 weeks – the lowest since June 2007.
Read MoreAverage London house double UK average at $750,000
"The latest survey reveals early signs of growing price resistance in the London market in the face of recent, rapid increases in residential values," said Richard Donnell, director of research at Hometrack.
Richard O'Donnell said London houses spent more time on the market in April, with sales taking longer to close and the proportion of markets in the capital registering price gains each month is starting to soften.
"Two thirds of London postcodes registered a price gain in April compared to an average of 76 percent over the final 6 months of 2013," said Donnell.
Read More'Unsustainable' boom in UK property to cool by 2016
"While these changes indicate very strong market conditions, they suggest that buyers are starting to become less willing to bid up the cost of housing at recent rates. Widespread media speculation over the sustainability of price increases in the London housing market is likely to be having an impact on sentiment," Donnell added.
Hometrack's study follows that of EY ITEM Club, which said it expects price growth in the "simmering" housing market to ease next year and to fall significantly by 2016 earlier this month.
Last month, the Bank of England, the Office for Budget Responsibility (OBR) and a member of the British royal family all warned of unsustainable rises in London house prices.
Read MoreUK inflation sinks to 4-year low, house prices surge
Heir to the throne, Prince Charles said the gains were causing a brain drain, as young people cannot keep up with rent payments.