Hi JK I think it's a Common Whitethroat but I could be wrong. Although the wings are in partial shadow I think I can see rufous tones on the back. Also, the underparts look quite beige, the wings too long and the bill too strong for a dumpy little Lesser Whitethroat. On a separate topic did you notice if the dragonflies were active? I didn't manage to get to Thursley last year. It's one of my favourite places for damsels and dragons.
There's a thread called Dazzling Damsels and Dragons 2020 if you want to post any photos.