The TaxPayers' Alliance said the Independent Parliamentary Standards Authority has demonstrated it was "not fit for purpose" after it published its recommendations to increase MPs' pay by 11 per cent.
Spokesman Jonathan Isaby said: "This unaccountable bureaucratic monster of a quango, which was supposed to help restore public faith in Parliament after the 2009 MPs' expenses scandal, has in fact just succeeded in turning the clock back four years.
"It beggars belief that Ipsa felt it an appropriate use of taxpayers' money to run up a bill in excess of £70,000 on opinion surveys, citizens' juries and focus groups.
"But it is beyond contempt that Ipsa completely ignored the very research which showed the public to think that MPs' pay is currently 'broadly fair'.
"The body which ought to be representing the interests of voters and taxpayers has unceremoniously put two fingers up at the lot of us."