As of today, I see that government guidance on the phased return to training for elite sports means all watersports, including sailing, windsurfing and kiteboarding are now allowed in England. However this is just for single-handing, or with members of your household, so double-handed or multi-handed crews who live apart cannot sail together as yet.
And it is recommended that boats sail in company, and support each other in case of need, in order to minimise risk of requiring RNLI or other emergency service assistance. So no single boats at this stage.
GPs can of course be sailed single-handed …
Oliver