Well...
Taxation has a significant effect on how much disposable income is in the economy. While Darling and Brown have been gifted a £15bn windfall in fuel duty receipts - remeber, they calculated their receipts based upon oil $50 per barrel, you could argue that taxes have increased significantly in real terms.

Remember that roughly 70% of the price of a litre of petrol is tax.

Then we have the abolition of the 10% tax rate, Car Tax rates being substantially hiked next year and also the fact that our energy bills are going to return higher tax receipts too.

The proportion of earnings being taxed has actually risen by 50% since 1997.

If taxes are visibly hiked further, the flow of money into the economy will slow to a trickle. This has the knock on effect of preventing people from spending, which means a dramatic fall in VAT receipts and Corporation Tax receipts from businesses who's products remain on the shelves.
(Bicycle Repairman "you're also a bit of a wanker", Fri 18 Jul 2008, 13:48, Reply)