Refusing to give MPs a pay rise will result in politicians stealing money, the Commons watchdog has suggested.
MPs must have a boost in pay in order to prevent a second expenses scandal and diminish the financial clout of lobbyists, according to Independent Parliamentary Standards Authority chair Sir Ian Kennedy, who said it was obvious that the previous system of lower pay and generous expense "would end in tears".
But he hit out at senior figures, including Prime Minister David Cameron, who have cautioned against recommending a big hike now - insisting there was "never a good time" to settle the issue.
The Commons expenses watchdog will defend the idea of handing MPs a significant pay rise
Sir Ian confirmed that Ipsa's initial proposals - expected to call for an MP pay rise of nearly £10,000 to £75,000 a year - would be published next Thursday.
He declined to reveal details in advance - although he did suggest that once the figure was fixed it would rise in line with average earnings.
His comments got a mixed reaction on social networks:
Sir Ian pointedly reminded "everyone, including leading politicians, that Ipsa was created by parliament to effect a clean break with the past".
"Of course, this is not a good time to be talking about the pa element of the package, save to notice that in the public sector pay increases are limited to 1% a year," he said.
"But given that there has never been a good time, this is as good a time as ever.
"Moreover, we know what happens when the element of pay is pushed aside as being simply too hard - the nods and winks school of public financing emerges, and ultimately we end up with circumstances like 2009.
"No-one wanted the system that brought parliament to its knees in 2009 to come into being, but it was the inevitable result of hard decisions deferred."
Speaking at the headquarters of the ippr think tank in central London, Sir Ian said the history of parliamentary pay was "a frequent rejection by the government of the day - with MPs, often reluctantly, falling into step behind them - of external bodies' recommendations that MPs' pay be increased".
"This rejection was coupled with a gradual engorgement of a system of 'allowances'.
"It was inevitable that such an approach would end in tears. The only hope for successive governments, all of whom knew that things were a bit dodgy, was that when the balloon went up, it would not be on their watch.
"The balloon duly went up in the summer of 2009."
Sir Ian said Ipsa was determined to treat MPs as "professionals".
In a clear message to party leaders - who have all indicated concern about big rises - Sir Ian stressed that "the power to set pay and pensions of MPs rests with Ipsa and with Ipsa alone".
A Commons vote is not needed, and "the Government does not get to pick and choose, there is no opting in or out".
"My hope is that, as the discussion is joined, political leaders will accept that we have a job to do which they gave us," he added.
"If they really do believe that pay and pensions should never ever again be the business of MPs, they should enter the debate with care and accept that external, independent regulation means what it says: that you do not tell the regulator what to do."
The new pay and pensions package is due to be implemented after the general election in 2015.
However, the extension of the 1% public sector pay cap means that MPs will potentially will be getting a 15% hike when millions of workers are receiving a real-terms cut.
Sir Ian said Ipsa was "impressed" by the idea that, once set, pay should rise and fall in line with "the fortunes of those they represent" - national average earnings.