I'm an Earl Grey man myself but occasionally I feel the urge for a mug of builder's tea.
In London the best place to avail yourself of these are the Cabman Shelters,of which there are 13 dotted around the capital.
I've never been asked if I'm a taxi driver so I presume it's okay for anyone to use them.
www.urban75.org/london/cabmans-shelters.html