Will they ever learn?

First there was cash for questions, then there was the Nolan investigation into standards in public life, then there was cash for honours, and expenses for moats and duckhouses and bathplugs and the like, and now, despite the many earnest promises by politicians to do something about it, we have new cash-for-access claims. It keeps on coming round, said the Deputy Prime Minister Nick Clegg, like some deeply unpleasant, unwelcome Groundhog Day. And every time it does, the already low reputation of politics sinks a little bit lower.

Both of the MPs involved in the new allegations, Labour's Jack Straw and the Conservative Sir Malcolm Rifkind, have denied, in different ways, any wrongdoing in the matter. Mr Straw, who was secretly recorded saying he could use his influence to change EU rules for a fictional commodity firm, said he had been scrupulous in following the rules, including on outside interests. Sir Malcolm, who is said to have claimed that he could arrange access to every British ambassador in the world, insisted any allegations of wrongdoing were unfounded. In due course, the Parliamentary Standards Commissioner will decide if they are right.

In the meantime, the whole unpleasant affair reopens the question of what MPs should be paid (and indeed what kind of MPs we want) and to what extent they should be permitted to engage in lobbying and other outside activities. The Coalition Government promised it would act on the subject of lobbying, and it has tightened the rules for former ministers (they now cannot lobby for two years after leaving office). However, the promised statutory register of consultant lobbyists has still to be implemented and the rules on who needs to sign up to the register and what should be declared are far from clear. That gap should be fixed as soon as possible.

In his response to the new allegations, the Prime Minister David Cameron said he did not favour the idea of cap on outside earnings because that would exclude someone running a family shop or family publishing business and there will probably be some public sympathy for that. Banning outside interests could accelerate the move away from the days when MPs came from a wider range of backgrounds and lead to more age-of-machine politicians who go through the familiar routine of politics degree-researcher-MP.

Is a cap on outside earnings the answer? It is not such a bad idea - the US Congress for example has a cap of around 15% of their regular earnings and Ed Miliband, the Labour leader, favours a version of that in the UK. But a better approach would be to finally tackle the issue of MPs' pay. Sir Malcolm's comments that it is unrealistic to expect someone to go through their parliamentary career on a salary of £60,000 will stick in the craw of many, particularly when it is so much more than the average UK salary of £26,500. But the pay of a backbench MP falls way below that of some secondary head teachers and many senior civil servants and in the context of central London, the disparity is ever greater. The danger of leaving pay at its current level is it feeds the monster that has led to the cash-for-access scandals. Longer term, the proportion of independently wealthy MPs could also increase.

Of course, only an incremental increase to MPs' salaries would be acceptable at a time when many constituents still face frozen wages, but a reasonable rise combined with clearer rules on lobbying could finally help the Commons move on from this terrible Groundhog Day it keeps on experiencing. It might also remind MPs what is expected of them: they should be paid well, but in return, they should be working full-time to represent their constituents, not a firm that is paying them a nice daily rate.