Mr Ahern has now given two different prices for the house he bought off Griffith Avenue in Dublin in 1997 shortly after he became Taoiseach.
In a statement to RTÉ's Prime Time programme last night, the Taoiseach's spokeswoman said Mr Ahern had paid £180,000 for the house in Beresford estate. "I can confirm that, as the Taoiseach told the Dáil today, that the purchase price of his house was £180,000, reflecting the market price of that time."
Prime Time reported that the Mayo-born businessman Michael Wall, who is based in Manchester, and from whom Mr Ahern bought the house, paid £138,000 two years earlier.
However, Mr Ahern in 1997 told Ken Whelan and Eugene Masterson, authors of Bertie Ahern: Taoiseach and Peacemaker, that he had paid £139,000 for the house.
Mr Masterson said he had a tape-recording of the interview, and that the Taoiseach had been given an opportunity to correct a galley proof of the book before it was published. The relevant section of the book reads: "It cost him £139,000 to buy and is today valued at over £200,000 in the highly inflated current property market in the capital.
"Friends say that it is the only time that he has come out on the right side of a balance sheet," it reads.
If pressed, Mr Ahern is understood to be ready to say he made a mistake during the interview with the authors. The price paid by Mr Wall for the house is not mentioned in the deeds, it is understood.
Mr Ahern rented the property from Mr Wall - who provided transport for people who attended the Manchester dinner at which he received £8,000 sterling in 1994 - for two years before purchase.
In the Dáil, Mr Ahern did not mention the £180,000 figure, but said he had furnished the Mahon tribunal several years ago with all the details about his house.
He claimed in the Dáil that Mr Wall had made a 30 per cent profit during the two years in which he owned the property, which is now worth some €1.4 million, according to local auctioneers.
He went on: "Mr. Wall would have had a gain of about 30 per cent in the 2½ years. I paid the full market value for the house and I funded it by means of an Irish Permanent Building Society loan."
