The sandy beach in Brighton is completely fenced off with a quick-shutting gate and dogs can run off leash all year round. The beach is very popular with dog owners and you'll always find some doggy friends there.
Free parking is very limited in the Sandown Street area and you will probably have to use the ticketed parking area in front of the Middle Brighton Baths. Parking in the area is ticketed 7 days a week including public holidays from 8am to 8pm.