A report today by a committee of MPs – and we know what high standards they have – blames the banks' bonus culture as a major source of the financial crisis. The remuneration system, they say, worked to encourage bankers to go out and make deals, without worrying whether they were good or bad deals. They got the cash either way. But naturally, a lot of the deals they engineered were indeed bad.

That's true. But what brought on this bonus culture in the first place? The cause is actually down to the political system.

For the past twenty years, politicians really have believed that they were saving us from boom and bust. Any time there was a blip in the market, like the 1987 stock market slide, or after Russia defaulted on its debt, or most spectacularly after 9/11 – they 'saved' the system by flooding the world with cheap credit. Interest rates after 9/11, for example, came down from 6.5% to just 1%. With credit six times cheaper, people of course borrowed a lot more, buying houses, shares, securities, any asset they could. So many people were buying, that these assets shot up in value.

The response of the banks' management was rational. In this boom atmosphere, almost everything succeeded. Buy an asset today, it would be worth more tomorrow. Since all deals seemed to work, they naturally rewarded staff who made more deals. Of course, when the bubble burst, they all discovered just how dodgy some of these deals were.

But when you are looking at the causes of this crisis, you have to go behind the bonus culture, and not just stop there. What caused that culture was not 'greed' by the banks. They didn't all suddenly get together and decide to be really, really greedy. It was the politicians who engineered the boom that made this perverse culture seem perfectly rational. Physician, heal thyself.