Horses for courses.
As you are probably aware, I see a lot of houses being bought, refurbished and sold, mainly repossessions, 'seizures' (ordered by Courts) or 'probate sales' etc., and it's pretty common that the electricity supply has been 'cut off' [by removal of cutout fuse(s)]. However, it's virtually always the case that when the new owner approaches a supplier for an electricity supply, they arrange for the supply to be 'reinstated' at no cost.
This is correct, but it seems
@Murdochcat is not looking at a domestic property, and also not going to own the property, he is looking at a change in use, so some of it may become domestic in the future, but since he, it seems, will not own the property, much depends on who was in the past libel for the bill? If the present owner was the name on the bill, then it will need paying before power is restored.
This is in the main a site about DIY domestic work, not how to go about doing work on commercial premises. I know where I volunteer they have a building which was start up premises for small businesses, and have multiple supplies, the cost of removing the duplicate supplies is about the same as paying the standing charge for 15 years, so they pay the standing charge, as still not sure what they will need in the future.
This is not how it would work with domestic.
So to try and guess what will happen is a bit pointless, as we have no idea about who owes the money. And the people who can work it all out, do not do it for free, citizens advice does not cover commercial, it is down to your solicitors to find out what will need doing. You're not going to find it all out for free.