I've visited Corton cliff top at night in the summer months. There are one or two couples who use this site, but a lot of men.
Have to park-up and walk into the clifftop wooded area.
During hot summer days the beach can have a few nudists on too.
The layby on the A120 near Coggeshall,
The layby near Levington off of the A12/A14, Nacton shores,
And the nudist beach near St Osyth, hope this helps,