Antique Victorian 1889 walker and hall silver top ribbed dressing table jar London lovely vacant cartouche and repousse decoration to lid some minor age related wear 
8 cm tall 
4 cm round 
An "M&W" silver hallmark is the maker's mark for the renowned British silversmiths Mappin & Webb. This mark, sometimes in a square or oval, is found on their sterling silver and silver plate items, and it is always accompanied by a full set of other hallmarks from the relevant UK assay office (Sheffield, London, or Birmingham), as well as a date letter, according to this Silvercollection.it article and this Mappin & Webb article on Wilson55.com. 
What to look for in a Mappin & Webb hallmark
Maker's Mark: "M&W" in a box or oval. Sometimes the maker's mark is on a separate stamp or a unique design like the "sun" trademark used by Mappin Brothers before they became Mappin & Webb.
Assay Office Mark:
Sheffield: A crown.
London: A leopard's head.
Birmingham: An anchor.
Date Letter: A letter of the alphabet that changes each year, indicating the year the piece was made.
Sterling Silver Purity Mark: A lion passant, which signifies sterling silver.
Duty Mark: For many pieces from the late 18th to mid-19th century, a profile of the ruling monarch is present.
Royal Warrants: Some pieces will also have a royal warrant, such as the Queen's head for Queen Elizabeth II. 
How to identify the date of your piece
To determine the date of your Mappin & Webb silver item, you need to identify the hallmarks that are present on the piece and then use them to find the corresponding year. Each hallmark corresponds to a different aspect of the item's history, including the maker, the date it was made, and where it was made.