What's with the 100 year lease? Why would anyone do that even if it were not a joke altogether?
Flats in the UK are often not sold as in the US, but rather you purchase a long term (100+ year) lease to the property with the option to extend essentially indefinitely (for a reasonably small cost). Some flats comes with a share in the freehold (ownership of the actual building), but at least in London those are fairly rare.