The ONS has admitted it is looking at updating its policy on revising its house price data after property market commentators questioned its accuracy.

Using Land Registry data, the ONS house price index last week said transactions had fallen 21.2% in November, but figures from HMRC for the same month show they fell just 7.1%

Lucian Cook, head of residential research at Savills, told the Telegraph: “The ONS index was trailed as a single definitive index for the UK housing market, providing more detailed information on transactions and house price movements at a local level and between different parts of the market.

“This was always going to be a huge undertaking, fraught with difficulty.

“However, it continues to be blighted by issues around accuracy and reliability. These have been sharply brought into focus by the growing discrepancy in reported transactions numbers compared to figures coming out of HMRC.”

The differences are blamed by ONS on a time lag at the Land Registry on when transactions are updated, which also means the actual average house price is often reviewed and revised down.

Chris Jenkins, house price statistician for the ONS, said: “We are looking to update our policy on revisions shortly. Hopefully we will put an update out with next release.”

It comes as buying agent Henry Pryor, who also questioned the differences in ONS and HMRC data, tried to ascertain what is actually driving the falling volumes in the market.

He said: “Perhaps the thing to concentrate on are the trends rather than absolute amounts.”

Using Land Registry figures, Pryor said home sales spiked in March, ahead of the Stamp Duty changes, but there has been no blip following the EU referendum vote.

This, he said, suggests Brexit hasn’t had an impact yet or isn’t an issue.

Pryor also adds that he doesn’t think house prices are the issue either.

He said: “What does seem clear is that there are about 40% fewer homes being sold each month. The latest data from Land Registry is for November by the way.

“Many people are blaming higher house prices on ‘a lack of homes for sale’ but if you look at the total number of homes for sale and annual house price inflation there doesn’t actually seem to be a link, at least not one that I can define.

“As I have suggested before, house prices aren’t down to simple supply and demand but to the cost and availability of credit.

“Cheaper mortgages for more people drives up prices paid for the finite number of homes that are available be it 1.2m in 2007 when annual house price inflation was 10%, or the 620,000 for sale today when prices are rising at 6.2%.”