Should only fail if..
A registration plate is:
a. missing or incorrect
b. so insecure that it is likely to fall off
c. letter or figure missing or incomplete
d. faded, dirty, delaminated, deteriorated or
obscured, (for example by a towbar) so
that it is likely to be misread or is not easily
legible by a person standing approximately
20 metres to the front/rear of the vehicle
e. background overprinted or shadowed with
text e.g. vehicle manufacturer name.