On a trailer at the back of the service hanger was a Spitfire 1a which looked spanking brand new. The serial Number was RG904 - Hang on.... these aircraft were numbered between R6595 and R7257, so an RG number is far too late for a 1939/40 production aircraft..... this warrants some investigation.
The serial number was originally allocated to a Miles Martinet TT1 target tug like the one shown below.
The penny dropped when I did an internet search to locate the serial number. These markings were used on the first Airfix model Spitfire kit (Known as the Spitfire BTK). It seems that this aircraft may be a recent replica painted up as a spoof to generate some conversation. The plot thickens.
I have a recollection of reading somewhere, a few years ago, about the RAF commissioning plastic replicas of Spitfires and Hurricanes to use as gate guardians on military bases. I have been unable to find any reference to this, but I wonder if this Spitfire is a spare one!
Of course it is the RAF Cosford Air Show on Sunday 14th June - perhaps this is an exhibit for that event.
Footnote: A week or so on and I have discovered that the Spitfire in question was a giant Airfix kit constructed for a TV show and built by James May and a group of children from a Telford school. It is a 1:1 scale representation of the Airfix spitfire kit. The program will probably go out in late October.