What pay and bonuses did the highest paid staff receive last year? What is the ratio between the pay (including bonuses) of the highest paid and lowest paid staff member?
While these sorts of statistics are sometimes published for individual banks, it is not easy to find sources in which the answers are collated. Move Your Money includes some information on high pay in its summary of mainstream UK banks. It may well be worth asking a bank about the pay ratio, which will at least reveal if it has even been calculated.