Nadine Dorries’s novels.  George Galloway’s TV presenting.  John Redwood’s writing of market reviews and investment reports.  Geoffrey Cox’s work as a barrister. All would end – and their begetters would perhaps quit the Commons in consequence.  Even as patriotic and dedicated a man as Redwood might jib a little at seeing his income slashed by three quarters or so.

The cause of their departure would be Ed Miliband’s proposed bar on MPs earning more than 15 per cent of their total income from outside interests.  And in consequence Parliament would be, literally, the poorer.  Able ex-Ministers would depart even more swiftly: I recently cited the case of Sir Hugh Robertson.  Fewer directors of family firms or active business people would enter Westminster. Many would leave. MPs would be professional politicians only – dashing through the revolving door to Westminster to gain Ministerial office, and then dashing out again in search of more money.  The only people who would remain would be the rich, the mad and those incapable of doing anything else.

This prospect has been brought closer, if Miliband becomes Prime Minister, by today’s story about Messrs Straw and Rifkind (which come at a very helpful time for the Daily Telegraph).  There is a difference between what rules oblige MPs to do, and what one they should do.  I think both men were wide of the second.  They will disagree.  The public will already have made up its own mind.

The one certainty is that, whoever is right or wrong, no law or rule can make people behave well.  This is not to say that there should be none at all.  But those that seek to make MPs do so have had unexpected consequences.  This has been so since the story of restrictions on their outside interests began with the register and proceeded through Nolan to the further changes pushed through by Gordon Brown.  We have moved much closer to a Commons of professional politicians, with their salaries and expenses paid by the taxpayer. These are no more popular than the generation that preceded them.

There is a choice.  The first option is the citizen legislator model of MP, under which they earn privately and aren’t supported by the taxpayer.  That would mean more scandals like today’s.  The second is the professional politician who is paid to do a full-time job as a legislator and is supported by the taxpayer to that end. He will have to be better remunerated if the quality of MPs is not to collapse.

Collectively, we don’t want to make that choice.  We want MPs who don’t earn outside the Commons and aren’t paid more by the taxpayer and are people of real ability. But it’s impossible to have all three at once.