Average house prices indexes may be on the rise, but the price of an average house is not.

That, unless I very much mistake it, is the message from the latest Hometrack survey, which in August measured the first rise increase in house prices since July 2007.

But as is well documented averages mislead and can disguise what is really going on, without recourse to lies or damn lies.

For instance, had the Ashes been won on the best averages, Australia would have won hands down this summer.

They didn't. I'm happy.

Anyway, after three months of no change, the Hometrack survey puts the average monthly price change in August at 0.1%.

But Richard Donnell, director of research, sensibly warns that if you take these figures at face value they can support the talk of green shoots, but there is a very different reality lying beneath the headline figures.

His analysis shows that the headline figure is being skewed by price rises in relatively small pockets of the market, mainly in London and the South East, where there is a lack of supply of houses for sale.

Usefully the Hometrack figures register which postcodes are seeing rises. And, actually, very few are registering price rises after a sustained period when prices were falling across the board. So pick a postcode at random and the chances are overwhelmingly that prices are not rising.

"There is a danger that an increasingly severe shortage of housing for sale in a relatively limited number of markets is impacting on prices and the headline performance of the housing market. This is creating the impression of a national housing market recovery," he says.

He later adds: "There will continue to be activity in the less mortgage-reliant parts of the market but a fully functioning housing market requires first time buyers and activity across a broader spectrum of would-be purchasers than we have at present."

Beyond the importance of this comment in relation to the functioning of the market, it has implications for the house price index numbers we see month in and month out. Because when we look at average house prices we have to remember that at any given time most houses are not being sold.

So the question is: How representative of all homes are those that have just sold and that are bundled up within the various house price indicies?

At the moment the answer appears to be: Not very.

And on the market generally, Richard takes the view that things remain fragile and warns that there is a real danger of a resumption of falling prices if there were to be a sudden reversal in buyer sentiment or increased numbers of homes coming on the market for sale.