Brown accuses two more Murdoch newspapers of hacking and fraud

The crisis engulfing Rupert Murdoch's global media empire dramatically worsened last night when it was claimed that private investigators working for The Sun and The Sunday Times targeted the former prime minister Gordon Brown.

In another extraordinary day in the phone-hacking scandal, News International's denials that illicit newsgathering techniques stretched beyond the News of the World came under strain in the face of well-sourced claims that two of its other best-selling titles were also involved in serious wrongdoing.

As Scotland Yard launched a fierce attack on News International for undermining its new inquiry into the alleged bribery of police officers by reporters, it was claimed that private investigators for Britain's largest newspaper group attempted to access Mr Brown's phone, medical records, and bank account.

Illegal attempts were made by a "blagger" apparently working for The Sunday Times to access Mr Brown's account at the Abbey National bank in 2000. In a letter to The Sunday Times' editor John Witherow, Abbey National's senior lawyer wrote: "On the basis of facts and inquiries, I am drawn to the conclusion that someone from The Sunday Times or acting on its behalf has masqueraded as Mr Brown for the purpose of obtaining information from Abbey National by deception."

Separately a tape obtained by the BBC showed a "blagger" identified as Barry Beardall seeking, also in 2000, to trick Mr Brown's solicitors, Allen & Overy, into handing over details of the amount he paid for a flat in Westminster. A claim that he had underpaid for the flat by up to £30,000 was the subject of a report in the paper.

In another case, in October 2006, Rebekah Brooks, then editor of The Sun, contacted the Browns, informing them that she had obtained medical details about their four-year-old son Fraser. The Sun subsequently published an article stating that Fraser had cystic fibrosis.

Police are thought to have evidence that the News of the World's private investigator Glenn Mulcaire had targeted the Browns. In a statement, the couple said: "We are shocked by the scale of law-breaking and intrusion into our private lives."

News International – whose chief executive is Ms Brooks – said it would investigate the allegations. The targeting of Mr Brown came as emails indicated that the NOTW had been bribing a Royal Protection Squad officer for personal details about the Queen and Duke of Edinburgh.

The police yesterday accused Mr Murdoch's company of undermining Operation Elveden, its new inquiry into alleged payments by the NOTW to corrupt officers. Scotland Yard said an agreement by NI not to make public details of internal emails outlining the claimed payments had been breached by the "continuous release" of information. They said it threatened to hamper the operation, which last week arrested the NOTW's former editor Andy Coulson. The alleged corruption involved about five serving officers.