The prime minister has been criticised for failing to uphold standards in public life by the sleaze watchdog he personally appointed.
The watchdog was set up after the cash for peerages row and in the wake of deputy leader John Prescott's affair with his diary secretary.
Sir Alistair Graham, chair of the committee on public standards, lambasted Mr Blair for thinking standards a "minor issue, not worthy of serious consideration".
In an interview with the Sunday Times, Sir Alistair said he was frustrated with the lack of support from Downing Street.
"I think it's a major error of judgement," he said.
With opinion polls showing voters considered the government sleazy, Sir Graham said Mr Blair may pay a heavy price for ignoring standards.
"We would have preferred more support from the prime minister. We suspect he is pretty lukewarm to the work we do," he said.
Sir Graham added chancellor Gordon Brown appeared more proactive in tackling the anti-sleaze agenda.
"I was pleasantly surprised how interested he was in the issues, I think that is a helpful sign," he added.