In relation to the allegations made today, a spokesperson for The Sunday Times said:

"We pursued this story in the public interest.

"We were told that Mr Brown had bought a flat cheaper than any normal valuation and that he obtained it through a company in which Geoffrey Robinson, a close ally, had been a director.

"We had reasonable grounds to investigate this matter and followed the PCC Code on using subterfuge.

"We believe no law was broken in the process of this investigation, and contrary to Mr Brown's assertion, no criminal was used and the story was published giving all sides a fair hearing.

"We also note that Allen & Overy, the law firm, have denied they handed over any details about the purchase of the property and had nothing to do with it."