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Just search ebay and you get examples like this Atkinson Brothers Of Sheffield Stainless Steel Canteen Of Cutlery | eBay . Also check completed items. All that may give you an impression of worth.
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That is the earliest I could see stainless steel used in British cutlery. I would agree with Butzy that it is likely much newer than that but an exact date is beyond me.

Bob

Can't do valuations as it is against forum rules and I wouldn't have a clue anyway. Can say it was made after the late 1800s as it is stamped England and not just Sheffield alone. Stainless steel was...