I am a British citizen residing in South Africa. In June I will be visiting family in the UK accompanied by my South African wife who holds a valid C Business visa (expiring in 2018). Under the new regulations, can my wife use her existing visa to enter the UK or must she apply for a new visitor visa?
This document on "transitional provisions for visitors" seems to say that your wife's business visa now functions as a standard visitor visa:
Unfortunately, I wasn't able to find anything stating this more explicitly.