Yates of the Yard to put record straight on cash for honours

The police officer who led the "cash-for-honours" investigation will detail Downing Street's alleged "obstruction" of his inquiry this week, in his first public appearance since the case against at least three of Tony Blair's inner circle was thrown out by prosecutors.

Assistant Commissioner John Yates will respond to long-running allegations that the former prime minister's advisers failed to co-operate with his own team as they attempted to substantiate allegations against aides accused of offering honours in return for huge financial contributions to Labour Party coffers.

Mr Yates, one of Scotland Yard's most senior officers, has told friends that he hopes to "put the record straight" and explain why his team failed to produce a winnable case at the end of their 15-month investigation into alleged breaches of laws governing the award of honours.

Members of a committee of MPs which will quiz Mr Yates on his inquiry this week have been told that he will be ready to answer searching questions about the conduct of his investigation and the Blair government's response to it. Mr Yates is believed to have requested a private meeting with the Public Administration Select Committee (PASC) but was told that the long-delayed hearing must be held in public.

He is expected to give further information on the diary entries seen as pivotal to his case, in which one businessman allegedly discussed a knighthood with Mr Blair's fundraiser, Lord Levy.

The Public Administration Committee has also been given free rein to question the officer over explosive allegations, including the claim that Mr Blair had threatened to resign if he was forced to be interviewed under caution, rather than as a witness.

Paul Rowen, a Liberal Democrat member of the PASC, said the committee had been primed to grill Mr Yates over the most controversial areas of his investigation.

"I want to know whether Assistant Commissioner Yates and his team got all the co-operation they were entitled to during their investigation," he said.

"Was there obstruction from Downing Street or Mr Blair, and why, at the end of the day, when it was clear that Mr Blair had driven a coach and horses through the honours regulations, were they not able to do anything about it? The public has a right to know – these people can't go around saying they have been found totally innocent of all the suspicions raised against them when we don't know what went on during the inquiry.

"Tony Blair has made a mockery of public life in the same way that Lloyd George did. We have heard allegations that he even threatened to resign if he had been forced to answer questions under caution.

"These are the things we need to ask and we are going to be asking: what pressures were put on, how co-operative was Downing Street and why did it take so long for them to get nowhere?"

The assistant commissioner's investigation, sparked by a complaint about the apparent links between Labour donors and the individuals Mr Blair put forward for honours, eventually cost more than £1m. Officers interviewed 136 people, including Mr Blair on three occasions, and arrested four of his associates. But prosecutors ruled in July that there was not enough evidence to press charges.

Mr Yates is expected to defend the conduct of his inquiry, and in particular the significance of "dynamite" evidence in the diaries of Sir Christopher Evans, the biotechnology tycoon and Labour donor interviewed during the investigation.

The journals are believed to concern alleged conversations between the multi-millionaire and Lord Levy about the possibility of an honour. But they were ruled inadmissible as evidence by prosecutors at the last moment before the investigation was dropped.

Sir Christopher has indicated that the issue did come up in conversations with Lord Levy, but says that there was never any agreement and the discussions were unrelated to his financial support for the Labour Party.

The committee will also hear evidence from David Perry QC, the barrister who advised against prosecuting, and a senior Crown Prosecution Service official.