Hoping someone will be able to help!
I have seen a listed (grade II) building that I want to buy and convert from offices into a house. It was originally a house, but has been offices for a few years. I understand I'll need a Change of Use Order, and Listed Building Consent.
Does anyone have any experiences of dealing with this sort of thing in Sheffield, how long it takes and how likely it is, etc? Cheers....

You sound like you will need an architect. In theory it is a simple process. Unfortunately it's a minefield if you have no experience, and of course that could make it VERY expensive.

If you want to just sound out your thoughts give the Conservation Section a call at the Planning Department.