Nick Clegg said the cash-for-access claims involving former foreign secretaries Jack Straw and Sir Malcolm Rifkind felt like "Groundhog Day".
"This keeps coming round, " said the Deputy Prime Minister. "Whether there is individual wrongdoing or not, the cumulative effect is to deepen public scepticism about how politics operates.
"My own view is all political parties would be well advised to immediately after the next general election get together and have a look on a cross-party basis whether the rules need to be changed."
MPs reject proposals for a ban on politicians holding paid directorships, consultancies or trade union roles.
Sir Malcolm Rifkind is to quit as an MP at the general election amid fresh pressure over cash for access allegations.