I don't see how it can be within the law, the employer is telling the employee to do something that is detrimental to their health - that must be illegal.
Apparently not.
I don't think it's reasonable to ask a woman to wear something which is going to harm her long term.
You can get some very smart low heeled shoes.
The high heel thing is all about power dressing and company image.
Personally I think if a company forces it on female employees then it should pick up the bills for private treatment of bunions and bad backs etc.
It's the sort of dress code you would get if you were a bunny girl