National Institute for Economic and Social Research director Martin Weale has been brought in to investigate the way the Office of National Statistics compiled its average earnings figures.

Treasury officials had been puzzled for some time at the pay data coming out of the ONS, which conflicted sharply with the evidence of other independent surveys.

Bank of England governor Eddie George uses earnings figures to help set interest rates

The ONS has also been forced to revise its earnings figures several times.

The Chancellor wants to know the reasons why because the the Bank of England uses that crucial information to help set interest rates and determine how much people pay in their mortgages each month.

Announcing the review in a letter to Commons Treasury Select Committee chairman Giles Radice, Mr Brown said that its findings, which should be completed within four to six weeks, would be published.

He said: "I am sure that you are aware of the recent revisions to the average earnings figures and I know that you share my concern that official statistics should be of the highest possible quality.

He went on: "You will know that the Monetary Policy Committee of the Bank of England has attached particular importance to the average earnings data as a key factor in its decisions (on interest rates)."

Embarrassment for ONS

The decision of the Chancellor to mount an external inquiry is an embarrassment for the ONS, which had already appointed Professor Ray Chambers, an expert in methodology based at Southampton University, to carry out its own internal investigation.

Mr Brown said he took the decision after consultations with Bank of England Governor Eddie George.

ONS director Tim Holt has promised to give "every assistance" to Mr Weale's inquiry.

He said: "It is vitally important that we do all we can to fully restore confidence in the average earnings index.