I got my file out with all the car documents in and the original bill of sale and several early invoices state the registration number as STO 879R.
Later invoices and MOT certificates say XGR 9 is the registration mark.
The car was taken off the road aound 1987, the car had an MOT when i bought it in November 2006 and the current number of TRR 676R. This is on the MOT and registration document.
Perhaps the previous owner - the car was in the same family from new (2 previous owners from new on registration document)so when they took car off road they took the XGR plate off and put it onto another car. Then when they re-commisioned the car in 2006 the latest number was provided. Only guessing.
TRR676R Speke Built 2.0L Tahiti Blue TR7
1969 Mk2 Vitesse Convertible
1997 Rover 800 Vitesse Coupe