The Land Registry, which records all completed property sales in England and Wales, has been recording the price of all property sales since April 2000, although the data now goes back to January 1995.

The survey features the end of the buying process when a transaction is registered.

The Land Registry is using something called Repeat Sales Regression to measure the change in prices over time. This means it only measures the change in the price of properties that have been sold before, to ensure a proper comparison.

Most sales are included, except for commercial properties and a small number of residential sales, such as those of council houses and council flats sold at a discount. Repossessions and property transfers following a divorce are excluded to avoid skewing the sample.

The Land Registry produces a monthly survey, and also provides a quarterly survey to the BBC News website. The proceeds of all the transactions are totted up, and then divided by the total number of sales to reach an average sale price.

Because it takes virtually all residential property sales into account, the Land Registry's figures can provide a unique insight into not only national but local prices. In fact, the Registry can provide an accurate picture of prices down to postcode level.

A similar survey is produced in Scotland by the Registers of Scotland.