WannaBe ..... I do see where you're coming from, but I can't quite ditch the notion that people who are "fortunate" enough to have a well paid job should contribute a little more to society. Maybe, given house prices, and the overall cost of basic living (fuel, utilities etc) in the UK, there's an argument for raising the lower tax band (on the basis that someone earning £40k these days would still be hard pushed to buy somewhere to live in, even using 4x salary) as the start of the 40% band isn't that high ??
Why do I think higher earners should pay more tax ? ..... well, I'm not sure I can articulate it very well, but I suppose it's about being a decent member of society and acknowledging that you are better off than most, and can therefore "afford" to contribute more. I know I'm not putting it very well. Frankly, I'd be pleased to pay 40% tax, because that would mean I was, at long last, despite years of hard work and study, earning enough to be in that category, and be taking more home as a result.
If there was a flat rate tax band across the board, my extremely rudimentary understanding of taxes tell me that this base rate would have to increase hugely from 25% (albeit under 40%) to break even. For lower income families, that's going to have an impossible to live by impact.