Celtic Plate (which was chrome not silver plate) was the trade name used by E J Leek Ltd of Birmigham. I imagine that in the same way that Abrahams of Birmingham were associated with Davidson's glass there were other companies doign the same thing with other manufacturers.
A photo of one of there adverts is attached. There is little known about them after 1937.
1929 Listed Exhibitor. Manufacturers of E.P.N.S. Cake Baskets, Sweet Dishes, Entrees, Vases, Tea-sets, Butters, Biscuits, Salads, Trays, Honeys, Tankards, Oak Biscuits, and Whiskey Barrels; Camel, Worcester and Royal Chinese Dragon Patterns in China Mounted Ranges. (Stand Nos.J.36 and J.61) [1]
1937 Listed Exhibitor - British Industries Fair. Manufacturers of Modern Electric Table and Standard Lamps of outstanding design. Specialists in all quantity production work in Chromium Plate or Silver Plated Articles. Exclusive designs at quantity production prices. (Stand No. Cb720) [2]