The head of the Priory rehab clinics has protested to the honours watchdog about claims that his nomination as a Labour peer has been blocked.
Dr Chai Patel says his reputation is being impugned
The BBC has seen Dr Chai Patel's letter to the House of Lords Appointments Commission asking for reasons for its reported objection to his appointment.
The Labour party donor was cleared of misconduct charges by the General Medical Council last year.
Reports say the commission has told Tony Blair to withdraw his nomination.
Dr Patel, of Oxshott, Surrey, had faced being struck off after being accused of running a care home in which elderly patients were allegedly mistreated.
But following a hearing last summer, the case was dropped after insufficient evidence was produced and he was cleared of professional misconduct by the GMC.
The head of the Priory has taken the unusual step of writing to the commission after newspaper reports claimed it had advised the prime minister to withdraw Dr Patel's nomination as a working peer.
In a letter obtained by the BBC, Dr Patel asks on what grounds the watchdog has decided not to consider him for a peerage and complains that his reputation is being impugned.
"If it is true about your advice on this particular situation, then I would urge you in common decency to have the courtesy of informing me just on what evidence you base your decision upon and your reasons for drawing your conclusions," he says.
He said he felt deeply honoured when Mr Blair proposed him for a peerage, but writes that he can now "neither be offered the opportunity to undertake public service, nor be able to defend my reputation in day to day life".
The development follows reports that the commission has launched inquiries into three millionaire Labour donors nominated for peerages by Mr Blair.
It has been reported that Downing Street may have to drop Dr Patel from its list of nominations.
Dr Patel says he now regrets giving money to the Labour Party and would not withdraw his name from consideration as that would indicate "that there's something wrong with me", he told BBC Radio 4's World at One.
The prime minister's official spokesman refused to comment on the claims, adding: "There is a process involving the appointments commission. We do not provide a commentary on that process. These things take time."
The House of Lords Appointments Commission is made up of senior politicians from all parties and is in charge of vetting nominations for peerages.
The commission told the BBC its role was advisory and said it provided confidential advice to Downing Street.
A commission spokesman said it was "not responsible for the recent stories about its work.
"They have only served to make the job of vetting nominees for the House of Lords more difficult and to cause unnecessary distress for those featured in them."