On Fri, 7 Aug 2009 22:27:57 +0100, "Graham Harrison"
wrote:

I was under the impression that Northern Irish plates were the way to hide
the age of a coach.


True; any plate without an age-related prefix or suffix will do.

With reference to coaches, one reason for using old registrations was
to escape the need to fit 62 mph speed governors (EU Directive). All
coaches registered after a certain date had to have the governor. But
coaches whose chassis had been registered before that date could
operate without a governor up to their legal limit of 70 mph.

So, at least for a time, there was a market in old coach chassis being
thoroughly refurbished for use under new coach bodies. The
registration went with the chassis, so what was essentially a brand
new coach that had some older (but refurbished) chassis parts could
operate legally at 70 mph. meanwhile, an identical body on a brand
new chassis was restricted to 62 mph (100 km/h).

I don't know if this still goes on, or whether the requirement for
governors has now been further backdated. But that is one of the
reasons why so many coaches have old registration numbers.