By Brian Wheeler
Political reporter, BBC News
Politicians on all sides have been falling over each other to say how "shocked" and "appalled" they are about claims former Labour ministers have been offering to influence government policy for cash.
Stephen Byers said he had overplayed his influence to an undercover reporter
With an election weeks away, they know just how bad this sort of stuff looks to voters already reeling from last year's expenses scandal.
And although it might be Labour MPs in the spotlight today, they also know that stories about alleged "sleaze" tarnish the entire political class. The Conservatives, when they were in power, also had their share of lobbying scandals.
The ex-ministers involved this time, Stephen Byers, Patricia Hewitt and Geoff Hoon, insist they have done nothing wrong - and although the story is embarrassing there is no suggestion that they have broken any rules, although Mr Byers is facing questions about some of the claims he allegedly made to undercover reporters about how he had used his influence in the past.
What it does do is raise questions about the many MPs who are leaving Parliament next month and their contacts who remain in government - and the regulation of lobbying.
There has been a growing clamour at Westminster to tighten the rules on lobbying - and to end the "revolving door" which sees ministers walk out of their departments into lucrative jobs with industry while they continue to sit as MPs.
At the moment, they have to wait just 12 months before taking up a post in their area of expertise. And although their job offers must be vetted by a committee for up two years after they leave government, they can choose to ignore its advice.
MPs are not allowed to table Parliamentary questions in exchange for payment - and they must declare any money they receive for lobbying work in the register of members' interests.
But they are free to advise their clients on the best way of changing the law in their favour and to set up meetings with decision makers.
In fact, there is a big grey area about what ex-ministers actually do for their corporate paymasters.
Because most lobbying activity happens behind closed doors, it is difficult to know how much influence it really has on government policy.
"Many of the self-professed lobbyists to whom we spoke explained that they do not usually lobby government directly, but instead advise their clients on how to do this themselves," said a select committee report into lobbying published last year.
But the report said it "stretched the bounds of credulity" to say, as some MPs have done, that they were not employed for their contacts in government.
"Part of the appeal of employing former ministers is the perception - accurate or not - that they will be able to offer access across government. This is particularly so when their party remains in government," the report found.
And Alistair Darling, in his exasperated response to the latest revelations, said it was not necessary for companies to pay former ministers to lobby for them at all - they should just put their case directly to government.
This was a clear dig at Stephen Byers, who has admitted he exaggerated the influence he had when he was filmed talking about the rates he charges to undercover reporters.
But also at the £2bn lobbying industry, where hundreds of ex-MPs, advisers and officials are employed by specialist multi-client firms.
Lobbying is a fact of life in most democracies and even campaigners against it are not calling for an outright ban. MPs must be allowed to make representations to ministers on behalf of their constituents.
Tamasin Cave, of campaign group The Alliance for Lobbying Transparency, said: "What is wrong is when it happens behind the scenes and when it is opaque. When the public can not see how public policy is being influenced then we have a problem."
The government last year rejected calls by the Public Administration Committee for a statutory register of lobbying activity, detailing the names of lobbyists, whether they are former ministers or officials, who is hiring them and the minutes of their meetings with decision makers.
Instead it gave the lobbying industry a final chance to get its house in order through self-regulation and vowed to publish details of ministerial meetings with interest groups.
A register would certainly have answered some of the questions arising from the revelations about Stephen Byers' alleged contact with ministers and companies, unearthed by the Sunday Times and Channel 4.
But campaigners are hoping the latest revelations will bounce the government into taking further action.
Labour has now pledged to include a statutory register of lobbyists in its election manifesto.
The Lib Dems also back far greater transparency as part of a wider clean-up of politics.
"I think people are so fed up with the way money and greed is corrupting our politics and it's why I've always said we need to go far further than reforming MPs expenses - we need to reform the whole rotten system," said Lib Dem leader Nick Clegg.
The Conservatives have said they would rewrite the ministerial code so ministers are banned from accepting lobbying jobs for two years after they leave office and anyone breaking the code would face losing their pension.
They say they would look at introducing a statutory register of lobbyists, although some in the party believe it would not have the desired effect.
Tory leader David Cameron shocked the lobbying industry earlier this year when he said it had got out of hand and was the next big political scandal waiting to happen.
But the fact is there will always be MPs and former ministers coming to the end of their time in Parliament, in search of an alternative livelihood, who find that their most marketable asset is their contact book.
And the clamour by lobbyists to sign up former politicians and advisers with links to the Conservative Party, in anticipation of Tory victory in the general election, suggests it is not about to go away any time soon.
Whoever wins the election, if they are serious about reform, will have a fight on their hands.