Tony Blair could be forced to resign if confidential material is published in a forthcoming biography of the Australian conman Peter Foster, it was suggested in a court case in Brisbane yesterday.

Mr Foster's lawyers launched an injunction in the Queensland supreme court to force a journalist to return thousands of computer files about his dealings with Tony and Cherie Blair, alleging the files contained damaging information about the Blair family and the run-up to the Iraq war. The court refused to grant the injunction and ruled that the issue would have to be resolved in a British court.

Mr Foster told reporters outside the court: "We believe if this material was published the prime minister will have to resign. I will not be known as the man who brought down a prime minister."

Mr Foster, who became infamous for marketing fake slimming cures in the 1980s, was at the centre of the 2002 Cheriegate scandal in which he was named as the go-between for the Blairs' purchase of two flats in Bristol.

At the time, he was the partner of Mrs Blair's personal assistant, Carole Caplin, but the Blairs have denied his claims that he was close to the family.

The computer files were taken from Mr Foster's computer during research for A Question of Deceit, a book about Mr Foster and the Cheriegate affair being written by Richard Shears, a freelance journalist who contributes to the Daily Mail. Mr Foster's lawyer told the court that the material should have been returned by Sunday night as part of a £500,000 deal Mr Foster struck in July for rights to the book, and claimed that the Mail was to publish the extracts from the biography this week.

However, suspicions about a publicity stunt were raised yesterday when the Mail said it had no plans to publish any of his allegations.

Mr Shears was unavailable for comment yesterday.