And here's some information on the legalities...
Taken from...
http://www.opsi.gov.uk/si/si2001/20010561.htm#sch2
And an email from the DVLA...
Taken from...
http://www.opsi.gov.uk/si/si2001/20010561.htm#sch2
And an email from the DVLA...
"I can confirm that your assumption is mostly correct and European number plates may be used legally on vehicles manufactured between these dates (1973 and 2001). Schedule 2 Part 1 also extends the 'European' facility to number plates fitted on vehicles manufactured after September 2001. However, the equivalence test would be carried out against the latest issued British Standard"