Good for you bloss.
And yes, as triximalixie points out we have been ignoring the National Insurance issue.
To repeat, because there is a maximum as well as a minimum earnings level for National Insurance, once you go above that maximum your rate for employees NI drops from 11% to 1%.
So effectively, as soon as you earn more than £770 per week (in 08-09) - or just over £40,000 per year, your marginal tax rate immediately drops by 10%.
Therefore, in 08-09 on earnings from £6k (roughly - above the personal allowance level) to £34,800k you paid 31% tax (20% income tax + 11% NICs)
From £34,800 - £41,000 you paid 51% (40% income tax + 11% NICs)
From £41,000 upwards you paid 41% (40% income tax plus 1% NICs).
I think this is right, but I would happily stand corrected if anyone is better at this stuff than me (not hard - wrong sort of economist, don't do numbers ).