MPs have been warned that they face “big changes” in their system of pay and expenses as the “snouts in the trough” scandal continues to undermine public confidence in politicians.

In declaring yesterday that things are going to have to change, Leader of the Commons, Harriet Harman, acknowledged that Parliament was being damaged by the controversy.

Indeed it is – and big changes are going to be necessary, not least because this has now developed firmly into a major election issue.

Tory leader David Cameron has been quick to declare that no Cabinet minister with a grace-and-favour flat will be able to claim a second home allowance. Good.

The Tories have by no means been beyond reproach when it comes to riding the gravy train, but Mr Cameron has, at least, signalled how he intends to apply the brakes.

Gordon Brown has commissioned a review, but it will not report until the end of the year.

That leaves us with a vague declaration from Labour that “big changes” are on the way, while Mr Cameron has been able to be specific.

By the end of the year, election fever should be hotting up nicely, and those changes really will have to be big to convince voters that the lid has been slammed on the trough.

Sleaze brought about the downfall of John Major’s government after the dominant years of Thatcher. It is threatening to play a significant part in toppling Gordon Brown’s after the dominant years of Blair.

We can almost hear Mr Cameron declaring that his administration must be “whiter than white”.