Here in the USofA, mobile providers PAY the owners of the buildings a substantial sum every month for the space used (antennas on the roof or sides of the building, closet square footage for the radio and computer equipment, etc).
Does this not happen in the UK? Building owners aren't compensated at all?
My neighbor has a 200' tower on his property. It went up in the 90s for one mobile provider and he told me then that he was getting $1k/mo from them. There are now two more providers, plus some police and fire radios on the tower. I suspect he's getting upwards of $3k/mo from them.
Side benefit: we get excellent mobile signal strength :-)
Side disadvantage: For a while, we had interference problems with our garage door openers. Problems went away when they upgraded the equipment, which seems to happen every few years