Well in America (according to my ex-history professor, anyway) a history undergrad degree is the most popular to go to law school with. Apparently the market for law jobs aren't good right now here in America, but it could be different in the UK, I have no idea. Another common route for humanities undergraduate people is to get an MBA but that's also something I know nothing about even in America, much less the UK. And an underrated option: a graduate degree in library science. Librarians aren't rich (even the law librarians, which basically get paid the most), but it's a steady job and stress free, as I've found out from volunteering at two different ones this summer.
UNT (university of north texas) here in America offers an online library science program and the total tuition price for all classes in the degree combined cost less than $10,000 US dollars. I have no idea what the price of secondary education is in the UK but here, that's a bargain.