Rams Head Antiques has dated this piece to the Georgian era.
The case has similar decoration and an equally beautiful depiction of Kenilworth Castle to the reverse. The reverse also features a charming heraldic bear to the lower left, as shown in the close up images.

Nathaniel Mills was a pre-eminent 19th century Birmingham based silversmith. He specialised in the production of very high quality vinaigrettes, snuff boxes and card cases such as this example. The so called 'Castle Top' pieces are highly sought after. A double sided card case such as this is an even rarer find.

The card case is fully hallmarked and dated 1827, at this time George IV was King of Britain. The case is in excellent condition throughout, with an attractive, antique patina to all of the silver. It weighs 93g or 3.28oz. It measures 7.25cm wide by 9.5cm high and 0.75cm deep.
Rams Head Antiques has dated this piece to the Georgian era.
You can view the stock and full dealer information on the Rams Head Antiques Profile Page