A/ they may not allow you to trail cables around their car parkThey don't need a charger, just a plug socket.
Plug in when you get there and charge (albeit slowly) while you work.
B/ you may not be able to park close enough to a socket for your cables to reach
C/ is that form of charging not incredibly slow?
D/ in cold or wet weather, this is the UK, they are unlikely to leave doors or windows open to thread a cable through