Holkham beach in Norfolk is fantastic, you can ride any time and don't need a permit.
West Wittering in Sussex is also supposed to be good but there are time restrictions.
You can just turn up but you need to know tide times and what times the local authority permits riders. Some areas have parking you can access and some don't. You don't need a permit as such but you may need permission to park.
Holkham is AMAZINGGGGGGGGG we went for a weekend break stay at Little Lodge which was just LOVELY deffo would go again.
But nearer to home there Hayling Island, Climping, West Wittering and Ferring beach... check tide times and parking.. Ferring we could park right on the sea front