quietly leaving
You mentioned that the cong held the freehold. Thats fine but doesn't mean the building hasn't been mortgaged! Not that it really matters, land values in the UK are stil sailing upwards and debt or no debt there will be a tidy profit for the WBTS!
However if they are moving to a leased property. That suggests a serious case of cost saving / downsizing. Leased buildings would mean paying outfitting costs and ground rent but no other costs.
It sounds like they were trying to do a sale / leaseback to free up cash! Its quiet common amought large corporations to reduce the money tied up in infrastructure and capital equipment. It can also be used by less scrupilious people to transfer money from company to another in a very grey way!
This money roundabouts games is like an accountants dream! The average person has no hope of understanding it.