Thank you for making your question to JustAnswer. My name is*****'m an Antiques Expert and I will try to help you with your particular inquiry. Please, don't hesitate to contact me any time or to make follow up questions if needed.
Mappin & Webb was founded in 1775 when Jonathan Mappin opened a Sheffield based silver workshop, then as now a major centre of the English silver trade. The reference W20230 corresponds to a 1960s piece, manufacturer using a triple silver electroplating process.
Regarding the value of your item, I have just perform a market research of similar sold items as yours. I performed the research based upon the most recent finished auctions and private sells, so the value given is the real market value of your item. This is the only way to know the exact value of your unit.
The value will be in the range of 50-70$.
I'm sorry if the value provided is not as high as expected but I have to be honest and professional with you so you won't loose your time and efforts.
Please, use the stars to rate my answer or let me know if I can help you any further!