To us, it's an obscure shift of tax law. To the City, it's the heist of the century.

In David Cameron we have a leader whose job is to quietly legitimise a semi-criminal, money-laundering economy

'I would love to see tax reductions," David Cameron told the Sunday Telegraph at the weekend, "but when you're borrowing 11% of your GDP, it's not possible to make significant net tax cuts. It just isn't." Oh no? Then how come he's planning the biggest and crudest corporate tax cut in living memory?

If you've heard nothing of it, you're in good company. The obscure adjustments the government is planning to the tax acts of 1988 and 2009 have been missed by almost everyone – and are, anyway, almost impossible to understand without expert help. But as soon as you grasp the implications, you realise that a kind of corporate coup d'etat is taking place.

Like the dismantling of the NHS and the sale of public forests, no one voted for this measure, as it wasn't in the manifestos. While Cameron insists that he occupies the centre ground of British politics, that he shares our burdens and feels our pain, he has quietly been plotting with banks and businesses to engineer the greatest transfer of wealth from the poor and middle to the ultra-rich that this country has seen in a century. The latest heist has been explained to me by the former tax inspector, now a Private Eye journalist, Richard Brooks and current senior tax staff who can't be named. Here's how it works.