Piggies, that would have been Gnat T Mk 1 XR541.
After an incident and barrier engagement at RAF Mona on 7 Feb 1978, it was decided not to repair the aircraft as the Gnat was about to leave service. It was then stripped of any useful spares and sent to RAF St Athan as 8602M for ground instructional use.
The aircraft was used by a Painters and Finishers course for practice, being painted as 'PF179' - presumably 179 was their course number.
Now at Bruntingthorpe and hopefully to be restored to ground running condition. A Google Images search for PF179 will provide a recent photo.
Of course 6 camouflaged Gnat single seat fighters were operated by the UK in the 1960s - and a couple still survive. XK724 is at Cosford, but the most authentic is XK740 now at Solent Sky, Southampton.