london taxis with a 'T' prefix plate

[helpmetoo]

i saw two of these the other day
are they pco test cabs?

[NORMANTHEDOG]

there are loads of taxis with a t prefix plate

[helpmetoo]

just to clarify, i mean the pco taxi plate on the boot lid, not the registration number
if there are loads thanks for the info, still dont know why they differ from the normal 5 x number plates?