The post town name is unhyphenated by Royal Mail. Because only the first 10 characters are given in Mailsort post town lookup tables, the lack of hyphens has the accidental benefit of helping to distinguish unpostmarked mail for WALTON ON THE NAZE from mail addressed to WALTON-ON-THAMES (which is officially hyphenated and has a lookup entry at "WALTON-ON-", though there is no entry for either town at "WALTON ON "). Royal Mail Mailsort Technical website