Wandering into abandoned buildings is difficult, dangerous and a civil offence. It becomes a criminal offence if you damage the building to gain entry.
If you are doing it commercially, you don't want to be wandering round with tons of kit, models, or whatever you a re shooting, as you will have to have your wits about you for security, property owners, etc.
Some places are available to rent for film / photo shoots if you contact the owners - I seem to recall there's at least one website that lists sites that do this. Alternatively, go and have a drive round and if you see anywhere, ring up whoever is trying to let / sell the place and see if they would contact the owner and ask if they'd agree to letting you in.
Alternatively, if that's not an option, do a search on 28dayslater.co.uk or derelictplaces for locations. Just don't join up and ask for locations and how to access them, you will be met with a torrent of abuse and have the thread locked / deleted.
I don't know any sites myself down there, as I tend to explore places in the north, but I hope this helps.
Andy