By Sarah Toyne BBC News Online business reporter

Plugging the gap between early indicator surveys and Land Registry figures?

The dizzying array of indexes that track what is happening to house prices in the UK has just got some official competition.

The Land Registry, Nationwide, Halifax, and Royal Institution of Chartered Surveyors, Hometrack, Rightmove and, most recently, the Financial Times, all produce their own guides to the market's health.

They are calculated on different assumptions, at different stages in the house buying process and, even when they are covering similar data, can show different conclusions.

But now the government has launched its own monthly house price index.

The Netherlands, Portugal and Iceland are the only other European countries that produce such an indicator.

The government is keen to point out its new official index is not meant to compete with existing indices.

But given that its creation follows calls from the Bank of England and the Treasury for an official monthly reading, will the new numbers provide the definitive measure - and gazump the rest?

Imperfect world

The government has produced a house price index since 1968, but on a quarterly basis.

The new report uses lending information from about fifty lenders, which is collected through the Survey of Mortgage Lenders.

Every other day seems to bring a fresh house price survey, but each often appears to contradict the last More on housing surveys

The sample size has grown in recent years to 25,000 completions, but that only accounts for 25% of the overall volume.

There is also a wide divergence in what information lenders will actually supply.

Some lenders may only supply 5% of their sample data, while others contribute every completion on their books.

Calculating the index on completions, rather than approvals, however, should make the index reasonably accurate.

This is because actual prices at the point of completion can often differ from the figure set when mortgages are initially approved.

But unlike the Land Registry survey - the most accurate indicator of housing sales - the new monthly index will not contain information on cash purchases, which account for about a quarter of the market.

The major drawback is that the new reading is not very timely. It will only appear two months in arrears.

Housing market watchers will also find it difficult to track monthly movements in the market.

The index will measure changes in house prices year-on-year, but the figures will not be seasonally adjusted for at least a year.

Extra information

The survey has some important benefits.

It will offer indices for first-time buyers and for former owner occupiers.

There will also be indices for the whole UK, the major regions, one UK index excluding London and the South East, and another excluding London.

And its data will stretch back to February 2002, so year-on-year inflation figures will be available from February this year.

South East dominance

Unlike the Nationwide and Halifax survey which are weighted according to transactions, the new survey depends much more on the total amount of money spent.

Relying on expenditure in this way will mean that London and the South East, where house prices are highest, will have a greater influence on the government's index.

WHAT THE SURVEY INCLUDES First-time buyers index Former owner occupiers index Regional index UK index UK excluding London index UK excluding London and the South East

As house prices are currently rising more slowly in London and the South East than in other parts of the country, the survey is likely to be more conservative than other indicators.

On past experience the government's most recent quarterly index has reported lower inflation than Nationwide's and Halifax's surveys.

There is a simple reason for the government's keenness to concentrate on prices rather than the number of transactions.

It is an indicator much prized by the Bank of England and Treasury.

It tells them just how much money is going into house-buying, and allows them to track it in pounds and pence over time.

In search of perfection?

The government is working on measures to improve its accuracy and speed.

The slightly less than definitive index A government spokesman

Developments in e-conveyancing should speed up the time for information to be logged with the Land Registry, which will make it easier for the government to use Land Registry data in the future.

And the National Property Database, currently under development, will provide better information about property types.

The government also plans to publish more house price information for areas such as commuter belts around the major cities.

In the meantime, it has to rely on the goodwill of mortgage lenders to supply the data - and hope that more will join in so its sample size can grow.

The government acknowledges that other measures still have an important role to play - especially as its new addition will take time to perfect.