Lord Levy has said he was "deeply disappointed" by the decision to arrest him as part of an investigation into allegations of "cash for peerages".
Lord Levy is a close friend and colleague of Tony Blair
In a statement, Tony Blair's fundraiser said the arrest was unnecessary and "entirely theatrical", as he had been willing to co-operate with police.
The officer heading the inquiry insists the arrest was "integral" to the probe.
John Yates told MPs it had enabled police to seize documents they needed to pursue their enquiries.
The row comes amid speculation the prime minister may be quizzed by officers - and news a left-wing Labour MP, John McDonnell is planning a leadership bid when Mr Blair stands down.
Lord Levy was arrested when he voluntarily attended a police station in north London on Wednesday.
He was released on police bail and was questioned further on Thursday. He denies all wrongdoing.
In a statement, the peer's lawyer Neil O'May said: "Lord Levy remains deeply, deeply disappointed that the police decided that they should use their powers of arrest for the meeting.
"Lord Levy has always been ready and willing to co-operate and to meet the police at any time of their choosing.
"He has always been only too willing, also, to provide the police with any documents that they might have needed, and he continues to do so."
Mr May said this underlined "that the arrest was unnecessary, disproportionate and, as has been described by others, entirely theatrical".
"The only result has been a media circus, which has distracted from the issues under consideration," he added.
He said Lord Levy hoped the police would "concentrate" on their investigation and "bring it to a swift conclusion".
"Although any allegations remain unclear, Lord Levy wants everyone to understand that he has not been involved in any wrong-doing or assisted anyone else in any wrong-doing.
"We want to emphasise again that Lord Levy has not been charged with any offence and is confident he never will be."
Earlier, Deputy Assistant Commissioner John Yates met the Commons public administration committee in private for just over an hour.
He is understood to have firmly rejected claims Lord Levy's arrest was a "theatrical" gesture - a suggestion originally made by former Home Secretary David Blunkett.
Committee chairman, Labour's Tony Wright, said the impression he had was that Mr Yates was conducting a serious investigation.
However, he added: "I don't think it was clear yet to any of the people involved whether it would lead to prosecutions or not."
He said the police were trying to work out "whether although it may be dodgy, is it illegal".
Mr Yates had refused to say whether Mr Blair would be interviewed, said Mr Wright, but told the MPs that the police "will go wherever the investigation leads".
'Share the lessons'
Mr Wright said the MPs were told police had so far interviewed 48 people, 13 of them under caution.
They also learned three people had yet to agree to be interviewed by police.
He said the police had stressed that the inquiry was covering both the main parties, and said more Conservatives had been interviewed than people from Labour.
"They expected to be able to bring their investigations to a conclusion by the autumn, certainly by October, and the CPS would make it a priority then to decide whether this was going to go any further.
"And finally, the police said whatever the outcome of this investigation, they'd be very happy to share the lessons of it with us, and to do that in public evidence session," Mr Wright told reporters.
Lord Levy's arrest came two days after it emerged that he advised curry tycoon Sir Gulam Noon he need not tell a Lords vetting watchdog he had lent Labour £250,000.