I agree Casdon. I think the lower tax allowance should be set at about £20k, with stepped increases between that and £150k, where there should be a significant rise.
Three bands is not enough. There is a huge difference in spending power between £50 and £100k, as there is between £12571 and £50270, so the lower and middle income bands should be merged with several smaller steps between them, starting at around £20k, which is two thirds of average. That way, someone on £22k would pay (eg) 20%, someone on £30k 22% etc, with nothing on the first £20k, all the way to £150k where the rate would be fixed at something like 50% of anything over that. Someone clever than I would have to do the sums to stop there being sharp rises though - it is wrong to have a sudden increase that makes a promotion cost someone money.