1 May 2009, Tamasin Cave

In a lively exchange between Alan Duncan and Harriet Harman in yesterday's expenses debate, Duncan described the tabled proposal for more public scrutiny of MPs outside incomes as "absurd".

Two thirds of Conservative MPs, just over a third of Liberal Democrats and nearly a fifth of Labour MPs hold second jobs. Lets be clear about who has the most to declare.

Take Alan Duncan. On top of his constituency work and his job as Shadow Leader of the House - and the odd (very odd) TV appearance - he puts in one month's paid work a year to an oil company. He was until recently also a paid director of a second company based in LA. One reason given for him quitting in December last year was "because others might think that it presented a conflict of interest".

That the public wants more information on where his priorities and loyalties lie is far from absurd.

The Conservative back benches were quick to join him in damning the idea. Sir Patrick Cormack said it was no concern of the public's whether Anne Widdecombe MP made private money from writing books, and that this was a slippery slope to having a House of Commons full of MPs with no outside experience. Others labeled it "intrusive" and cried lunacy at the thought that every single bottle of wine accepted by an MP would suddenly have to be publicly declared.

Let's be clear that the public's concern does not arise from MPs moonlighting as authors. Nor did the proposal attempt to cover gifts. The concern is the potential for conflicts of interest, privileged access to public officials and undue influence on policy from private interests. It's a concern that will not be answered by simply knowing when MPs are clocking in and out, as proposed in the motion. It's about knowing what, for example, a nuclear power company that pays an MP £100,000 a year, is getting for its money. On this, the public has the right to far greater transparency.

Just a skim of the shadow cabinet and ministers is enough to show the potential for conflicts of interest: the shadow minister for Corporate Governance, who led the Conservative position on the Companies Bill, works for a law firm that lobbies for the private equity industry (they've referred to him their "inside track"); the Chairman of the Policy Review is a paid director of a banking group; the shadow business secretary is a paid advisor to a private equity fund.

When proposals for another transparency measure - a mandatory register of lobbyists - were first mooted by the Public Administration Committee last year, it too was greeted by objections from Conservative MPs that it would be an unworkable bureaucratic nightmare. There were echoes of this in the House today. It seems that any proposal to shine a light on the dealings between business and public officials sets Tory alarm bells ringing.

Latest: The vote to declare details of all outside earnings was won by a majority of 274.