Higher rate (40%) tax payers therefore only pay £3,000 for a £5,000 season ticket (less if you include NI and other deductions)
My effective marginal tax rate because of this (income between £50k and £60k) is 60% -- 40% income, 2% NI, 18% reduction in child benefits. The company has to pay employer NI too. That means for every £1138 they spend on a payrise for me, I get £400.
While my income is in the top 10%, our household income is pretty average for people with 2 children because my wife only works on occasional freelancing projects to keep fingers in the pie (say 10 days a year), and I work from home the majority of the time - we don't want to outsource the upbringing of children. If we do pay for child minding, it's an inlaw, which means petrol costs and a bottle of wine - which all comes out post-tax, so doubles in price compared to sending kids to a factory tax free (or "childcare").
It's also a case where those who can afford it more easily and can also afford London rent get discounts while people that earn less do not.
At least, in none of the companies I've worked for has it been pre-tax