Cost of living
UK tax rate is (quite a bit) higher -- but don't forget, for our taxes in the US it basically pays for the military wasting so much cash, road repairs, police, fire and ambulance (although many can't afford to actualy *use* the ambulance).
No free or cheap medical care so people either buy insurance or take their chances on being bankrupted by medical bills, or both since insurance refuses to pay sometimes (and the bill that was supposed to provide it has the coverage removed -- it taxes existing insurance to pay for, well, something, but that something was removed as a "compromise". It will fine people who don't buy insurance though!)
The "dole" here is screwed up, people have to make very close to 0 and in a lot of the country it only pays for a short number of months, if someone can't find a job by then too bad.
College? Better take out a huge loan, no assistance there (at least from the gov't -- colleges do have scholarships).
Finally, there's Medicare and Social Security, which are taken both from my paycheck (well when I had a job) and another portion paid by the employer (that money doesn't appear from nowhere, so basically . they send money straight to them in lieu of even putting it on my paycheck). As a bonus, at present Medicare and Social Security should be bankrupt by the time I'm old enough to be eligible to use them! I was making like $20,000 a year, and 40% was being pulled out in taxes, medicare, and Social Seucrity -- probably 50% when you count the employer's cut (which didn't show on my paycheck since "they" were paying it and not me). Higher income people do have even more pulled out. No insurance.
Anyway, I won't claim $75,000 = 50,000 pounds, but the high tax rate you pay has to be balanced against actually getting some services for it that people here have to pay cash money to get.