Public confidence in MPs fell steeply between 2008 and 2010, research by the standards watchdog has suggested.
The percentage of people in England who think MPs are dedicated to working well for the public dropped from 46% to 26%.
The Committee on Standards in Public Life said its survey indicated concerns "with self-serving behaviour" by MPs overshadowed other issues.
The watchdog said it would be "strange" if the expenses scandal had not contributed to public unhappiness.
Four former MPs have gone to prison for expenses fraud while a fifth has been charged but is yet to stand trial.
The watchdog's survey of 1,900 people was carried out in early 2011, 19 months after the MPs' expenses scandal broke.
Although it shows a "long-term decline in public confidence in those holding public office" since 2004, the report says that on many issues, the decline since 2008 has been even "steeper".
It suggests there has been no "bounce" in confidence since the new government came to power - or if there was one it was short lived and died out before the survey was conducted.
"Public satisfaction with the conduct of MPs has declined on every measure except taking bribes since the last survey was conducted," the report said.
Other findings included a drop in the number of people who believe MPs are competent, from 36% in 2008 to 26% in 2010, a reduction in the number of people who think MPs set a good example in their private lives from 36% to 22%, and a fall in those who think MPs tell the truth from 26% to 20%.
Fewer people also think MPs make sure public money is spent wisely.
The public attitudes survey lists 10 qualities considered important in an MP - including being dedicated to doing a good job for the public, not using power for personal gain, telling the truth and owning up when they make mistakes.
But only on "not taking bribes" did a majority of people - 67% - believe that all or most MPs exhibited that quality.
On each of the other nine, fewer than 40% of people interviewed in England believed most MPs had those attributes.
The report says it suggests concerns about bribery, or about "outside influence" on politics "have been overshadowed by concerns with self-serving behaviour on the part of MPs".
While the committee says it is not possible to say with certainty what lay behind the trend "it is possible that the expenses scandal has had an impact on people's views and appears to have fed into and exacerbated the long-run trend of increasingly negative evaluations of politicians".
People who supported one of the three main parties were more likely to believe standards were high among politicians.
The young, people from ethnic minorities and those in higher paid jobs tended to have more trust in MPs in general.
The survey was carried out before the latest escalation of the phone hacking scandal - and suggests that confidence in TV news and newspaper journalists has slightly increased since 2004.
In terms of who people trusted to tell the truth, "MPs in general" were ranked higher only than tabloid journalists. However, confidence in "local MPs" was far higher.
'Telling the truth'
Committee chairman Sir Christopher Kelly said the results made "stark reading".
"The public has a quite straightforward, common sense and relatively sophisticated, in my view, view of what they want from politicians and it is things you might expect," he told BBC Radio 4's Today.
"It is telling the truth, it's owning up to mistakes, it's trying to be in touch with what the public think and it's using money wisely; these are the things which the public expect."
He also warned parties not to duck the issue of reforming political funding.
Donations - particularly those of more than £100,000 - were a source of "major concern" to the public, he added, as people believed they led to "special favours" for donors.
"It would be a mistake for anyone to think this issue had gone away," he said.
"I firmly believe that the opportunity it offers to deal with this issue proactively, before another funding scandal forces change, should be taken."