I bow to your superior knowledge. From Wikipedia:I believe they retained that for a while after
In 1979, production of Raleigh 531 butted-tube bicycles reached 10,000 units a year. In 1981, the former Carlton factory at Worksop closed after a vote was held. The original decision to continue at Worksop was reversed but the management decided to go with the original decision, and by the autumn production was moved to a Lightweights facility at Nottingham. However, all bicycles made there afterward still carried the W for Worksop frame number designation until early 1990.