Two separate outfits are being confused here.
First, the Kestrels at West Raynham were flown by the Tripartite Kestrel Evaluation Squadron, in 1965-66. There were 9 aircraft, 3 each funded by the UK, US, and West Germany. The pilots were not TPs, they were all fighter pilots from the 3 countries involved. The boss was Wg Cdr Dave Scrimgeour, I believe. The intention was to evaluate the aircraft and develop operating methods and tactics for a VSTOL aircraft.
They had all gone by the time I arrived at West Raynham in the Summer of 1966. From then until Spring of 1969, WR hosted 1 & 54 Sqns with Hunter FGA 9, and 41 Sqn on the E side of the field with Bloodhound Mk2.
Then, about May 1969, the first Harrier GR1s arrived, along with the Harrier Conversion Team (3, later 4, RAF pilots) to start the conversion of 1 Sqn from Hunter to Harrier. Some flying was done at West Raynham before the whole Harrier operation moved to Wittering.
The inverted Harrier in the cabbage field was indeed Syd.