This is an interesting special purpose lock for sure. Even better that it appears to be in perfect condition.
This lock was made before its Patent was obtained (later similar models include the date 'January 1881'). Probably made by Thomas Turner & Co of Wolverhampton (a quality manufacturer), whose name is on the later patented locks. Fine all over nickel plating, possibly over brass. Not original key only works occasionally, but is included. To lock, the plunger is pressed down, after enclosing the assembly around the bottle top. The plunger springs open when the key is operated. An excellent and unusual antique lock - quite heavy to the feel. 2.1" (5.3cm) high x 1.5" (3.7cm) diameter - very collectable. - eBay (25 Nov 12)
This lock had a high bid of 64 British Pounds (Plus 5.60 Pounds Shipping).-----