Brit here,
You'll only really find the 'black cabs' in London (theres are tons) and some other major cities like Manchester, Liverpool, Birmingham etc etc.
ANY car can be used as a taxi here all is required visual is a light up taxi light sign on top of the car (held on by magnets i believe) and a liencsed registration plate that go UNDER the normal number plate. thou you'll find the 'people carriers' (6-8 people) will have lights built into the cars facing forward like the classic black cab
heres some taxis in my area: