The badges on those Chipmunks are, I'm pretty sure, ULAS markings. I'm also reasonably sure that ULAS was on Summer Camp at RAF Manston in 1974.
I might be able to confirm that on Sunday at the ULAS fly-in/drive-in at Old Warden aerodrome.
ULAS Summer Camps in my time were:
1970: RAF Thorney Island (also RAF Tangmere for circuits)
1971: RAF Marham (also RAF Watton for circuits)
1972: RAF Newton
1973: RAF Abingdon
...
1990: RAF St Mawgan
1991: RAF St Mawgan
1992: RAF Benson
Is there a ULAS in the house? Can anyone fill in the gaps* from 1974-1989?
*(This is not an invite for UWAS 'lads' to commit violence - they'll understand the meaning of that!)