I've used sea feeders with luck for flatties in not too streamy water or from pier/close range fishing. In the most obvious case I caught most of the fish even though my fishing mates stood ten feet to the sides of me. Mashed boiled shrimps with fish oil and mashed common mussels has given best effect. Also check the surf feeders at Sharnbrook tackle, use pulp of the same as your bait. The scent trail seems to attract especially cod and flatties. Must be said I fish in Norway, but I guess my experiences can be transferred to British conditions.