Woodbridge Antiques has dated this piece to the 1930s.
The inside of the band bears the clear mark for 18ct and PLAT.

A lovely ring in great antique condition.
Measurements: Ring size: R 1/2 Width across setting shoulder to shoulder: 2.1 cm
Depth of setting: 8 mm Width of band at base: 1.5 mm Weight: 4.1 grams
Weights and measurements are approximate.
Stock Code 42236
Woodbridge Antiques has dated this piece to the 1930s.
Specialists in quality antique silver, fine jewellery & accessories
You can view the stock and full dealer information on the Woodbridge Antiques Profile Page