Is this sterling silver or plated? How much? Thanks

It’s sterling silver and bears a Sheffield hallmark with the date letter u for the assay year 1912/13. The maker is William Hutton & Sons Ltd, a well-known and prolific Sheffield company.

You don’t say how big it is but 3-piece tea services of about the same age are selling on Ebay from around £250 for a bachelor (1-person) set up to about £600. (Prices are in GBP if the currency sign does not display properly.)