When the Conservative MPs Neil Hamilton and Tim Smith were revealed to have taken cash from the former Harrods owner Mohamed Al-Fayed to ask questions in the House of Commons it caused a public outcry.

Hamilton lost his seat to the TV journalist-turned-sleaze campaigner Martin Bell, and the scandal led to the creation of the Nolan Committee on standards in public life.

In the 15 years since "cash for questions", the House of Commons has cleaned up its act significantly.

MPs are no longer allowed to lobby for any organisation with in which they have a financial interest.

Or in the language of Parliament, it is "inconsistent with the dignity of the House" for an MP to "advocate or initiate any cause or matter on behalf of any outside body or individual in consideration of any remuneration, fee, payment, or reward or benefit in kind, direct or indirect".

And the penalties for transgression are severe – as the former MPs Stephen Byers and Geoff Hoon found out when they were secretly recorded talking lobbying services they could provide after they stood down as MPs.

But a few hundred yards away from the green benches of the House of Commons, things are rather different. In the House of Lords – which still debates, votes on and influences legislation – rules are less clear.

Yes, peers have to declare their financial interests in the Register of Interests but beyond that it is a free-for-all. One senior Liberal Democrat described the scene in the lobbies and bar of the Lords on occasion as being like a "lobbyist's convention".

Even the Tories accept there is a problem. One said, when the Blencathra case was raised with him: "Oh he isn't the only one."

Blencathra says that he is meticulous in ensuring that he has no conflict of interest between his Cayman role and his duties in the Lords. But he shouldn't have to be. The rules should be clearer in not allowing a conflict of interest in the first place.

Their lordships should grasp the nettle and sign up to the Commons rules on lobbying. Those who refuse should be able to keep their title but stand aside from the legislative business of the house.

It is a simple point: law-makers should not also be lobbyists.