I think some pps on here think we're talking about one room for Harry.
I don't know how many people would be in his entourage, but I'm sure it would have meant a huge operation for BP, especially since the building is out of use officially at the moment. It just won't be staffed, kitchens will have been shut down etc etc.
There'd be Harry (who knows, even Meghan and the kids at one point), PR people, personal assistants, nannies, security staff, admin people, secretaries...you name it. It would be a major operation accommodating them, and you can bet that both H & M would have been very particular about their demands - and made all kinds of rules about BP staff having contact with them 'for securiddee reasons - for the kids' etc.