I tried to flag down a taxi the other day, but it did not stop, are they not allowed to pick up fares on the road?

Not all taxis are permitted to stop and pick up fares from the street or ranks. There are two different types of vehicles; "Hackney Carriages" and "Private Hire"."Hackney Carriage" taxis are the only ones permitted to pick up fares from the streets or ranks. "Private Hire" vehicles must operate on the basis of pre-booked contracts.