MIG wrote:

I must be being dim, but how would a bus company benefit from
disguising the age of a bus from the casual observer? The individual
in the pub car park might not want people to know the age of his car,
but I can't see an equivalent motivation for a bus operator.


Perhaps an old registration number (perhaps with some matching "old"
content) allows a bus operator to escape the latest regulations, such as
those on emissions?

For some years, it was standard practice in coach companies to use old
registrations to avoid having to fit the 100 km/h (62 mph) speed
limiters that were required by law on all new coaches. That led to
varying amounts of "old" content in otherwise new vehicles, including
some suggestions that the only "old" part was the plate stamped with the
chassis number. ;-)

I don't know whether that practice is still common, or indeed possible
under the law. But I can understand coach operators wanting to be able
to operate perfectly legally at 70 mph. There never seemed much sense
in physically limiting coaches to 8 mph less than their legal limit.