Three people are likely to face criminal charges arising from the 11-month police investigation into claims that Downing Street improperly offered honours in return for donations.

Crown Prosecution Service lawyers have received files from the police indicating that charges should be brought against three people, although the inquiry is continuing.

“I would be very surprised if they are not charged,” a prosecution source told The Times. The same source said that Tony Blair was likely to be interviewed by the police for a third time because he had yet to answer certain questions.

The three whose position is most serious are those who have already been arrested during the inquiry. Lord Levy, the chief Labour fundraiser and Mr Blair’s Middle East envoy, was arrested twice: in July last year in connection with the misuse of honours and last week, over allegations of perverting the course of justice. Ruth Turner, the No 10 director of government relations, was arrested last month when police called at her home at 6.30am and questioned her for four hours, on suspicion of perverting the course of justice as well as the alleged misuse of honours.

Sir Christopher Evans, the founder of Merlin Biosciences, who secretly lent Labour £1 million before the 2005 general election, was arrested last September. He is the only Labour donor to have been held during the investigation.

All three were released without charge and have insisted during the inquiry that they had done nothing wrong.

Mr Blair’s position, which is already precarious, would be greatly weakened if any of his aides or advisers were charged and MPs asked privately yesterday whether he could remain in charge while people working for him were awaiting trial. Some suggested that Mr Blair should make a statement soon confirming his departure date, arguing that if he had not done so when charges were brought he risked the appearance of being forced from office in humiliating circumstances.

The investigation is still expected to end next month, when final files will be submitted to the CPS. The police are still awaiting information from Mr Blair, hence the likelihood of a third interview with him.

When questioned by detectives for a second time on Friday about allegations that some of his staff or advisers sought to pervert the course of justice, Mr Blair told them that he could not immediately provide answers to some of their questions. He undertook to get back to them in due course.

A CPS source said that the case had been strengthened by the testimony of John McTernan, the Prime Minister’s director of political operations, who gave a different account of discussions about honours from that given by other Downing Street figures questioned.

Mr McTernan angrily dismissed speculation yesterday that he had supplied the police with a personal diary, saying that he did not keep one, nor had he acted as a “mole” within Downing Street, alerting the police to deleted e-mails and other evidence.

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