'TWU' work was actually carried out by JFACTSU - 'Joint Forward Air Controller Training and Standardisation Unit'. In 1976 they had 3 JP4s, one of which (at least) was re-painted in camouflage colours. They were used to train FACs - often near Templeton aerodrome. Low level attack profiles were flown at half-Hunter speeds (210 KIAS) to get the army chaps ready for the later part of the course. I went for trips in both XP547 and XP564 in July 1976 after finishing my TWU course on the Hunter.
I understand that the JP4s ran out of fatigue not long afterwards and were then replaced with JP3As (the worst model ever - all the lack of performance of the JP3 and 150 lb heavier!). I don't think that the JP3As were ever camo'd; their JFACTSU role was taken over by the Hawk not long afterwards.