TAXI/MINICAB FIRMS with Car Seat Options
Important point to note: it's legal to travel in black cab without car seat (although wouldn't exactly say it's safe)
The taxi firms listed below are known to supply car seats, but need to be prebooked normally. Recommended by local mums on the facebook group.
Airport Only. 02071180110
Simply Airports. 02077014321
BA Transfer. 02089002299