No such changes have yet been made, and economists say under-reporting inflation data means Argentina is short-changing the holders of 40 per cent of its foreign debt held in inflation-linked bonds. One former Indec chief said that translated into about $500,000 (€344,000, £256,000) for every percentage point of inflation.

They also say other data using inflation as an input – including poverty figures based on the price of a basic basket of goods whose cost is no longer clear – have been muddied.

The IMF, which is due to conduct a review of Argentina’s economy, last week asked Indec for clarification of its inflation methodology.

On Monday the fund declined to comment on Indec’s response to its queries after Argentine media reported that Indec chief Ana María Edwin refuted every concern raised by the fund. Indec had no immediate comment.

Argentine officials lay much of the blame for the country’s 2001-02 debt and devaluation crisis on failed IMF policies in the 1990s, but the government looks likely to need the fund’s blessing to renegotiate its $6.2bn debt with the Paris Club of creditor nations.

IMF spokesman Masoud Ahmed last week reiterated points raised by Dominique Strauss-Kahn, managing director, in Buenos Aires in December, saying: “Reliable data on key economic indicators such as inflation are vital to forming solid economic and monetary policy.”

In January, Ms Edwin defended official data as “absolutely trustworthy” after dissident Indec workers published their own 2007 inf-lation estimates of between 22.3 per cent and 26.2 per cent – up to four times the official 8.5 per cent rate.

Indec last week reported prices rose 0.9 per cent in January compared with the previous month. Market expectations had been for a rise of up to 1.5 per cent.

“Indec’s performance is just a joke. It started as a little lie and it’s snowballed,” says Eduardo Fracchia, director of the economics department at Argentine business school IAE.

Surce: The Financial Times - By Jude Webber in Buenos Aires