All new MPs should be expected to attend ethical training, a standards watchdog said after finding evidence the House of Commons was lagging behind other pubic bodies in providing proper induction.
The chairman of the Committee on Standards in Public Life warned the Prime Minister that making sure politicians are aware of their duties to be honest, open, accountable and selfless "cannot be left to chance".
Too many though appeared to be skipping what training was on offer despite Westminster sleaze scandals and the new power for voters to "recall" wrongdoing MPs meaning "the stakes have never been higher" to preserve their public reputation, he told him.
A report by the committee pointed to reports that fewer than one in five of those elected for the first time in 2010 attended even one induction session, and one on dealing with ethical dilemmas was cancelled when too few signed up.
It said it understood that the issue was "delicate" as many elected representatives saw being taught ethics as " impugning their integrity and their common sense".
Others considered it an unwelcome assumption that unelected people were " in a better position to know what to do than are representatives who are elected precisely to exercise their judgment on matters of controversy", a study it commissioned into the issue concluded.
But chairman Lord Paul Bew said action was needed to ensure Parliament caught up with higher standards in town halls and the civil service.
"Of particular concern to us was the reported lack of engagement with induction by large numbers of Members of Parliament," he said in a foreword addressed directly to David Cameron.
"With the prospect of a Recall Bill, which will give the public the power to remove MPs who have behaved in ways that fall short of the standards expected of them, the stakes have never been higher.
"In effect, ethical issues will now be under even greater scrutiny. More than ever, MPs need to be fully aware of the principles and the rules that guide their behaviour.
"Parliament and the political parties need to provide the opportunities for them to build that awareness and understanding.
"An induction programme that fully embraces ethical standards should be the first of those opportunities."
The Commons was "noticeably behind some other organisations in embracing either the principle or the practice of induction, let alone accepting that there was a role for ethics within it", the report said.
If not compulsory, it concluded, induction programmes including ethics should at a minimum be " the norm rather than the exception" as it was "essential to ensure that public office holders are aware of the standards expected of them".
"We do not believe that ethical standards can be an optional extra for those in public life or that the value of embedding ethical standards can be overlooked," the committee said.
"We would especially like to see more of an obvious demonstration of leadership in relationship to ethical standards from those in the Westminster Parliament, both elected and appointed.
"Parliament sits at the apex of public life, legislates on standards for others in terms of regulatory regimes, holds to account those who fall below public expectations in terms of those regulatory regimes, and calls for standards to be imposed where it believes they are necessary.
"When it comes to ethics in practice, Parliament should lead by example and expect to be judged by the standards it imposes on others."
The report is part of the committee's submission to an inquiry being carried out into standards procedure set up amid controversies over the way MPs self-police misconduct in their ranks, notably in the case of the expenses scandal surrounding then cabinet minister Maria Miller.