One success story is the City of London Distillery, opened in the city centre in 2012 by distiller Jonathan Clark, who once worked as a dishwasher in the same building before working his way up.

The distillery owns two coveted large copper stills made by the Germany family company CARL.

Named Clarissa and Jennifer, the gleaming pear-shaped giants and a bottling and wax-sealing operation work away in view of the bar where customers sip gin cocktails.

Mark Butler, 50, who has 20 different gins at home, came for a class on gin-making to celebrate his birthday.

"I discovered it three years ago and I love it," says Butler, a commercial manager at a small football team. "I started looking at the traditions of the English gin and got interested."

Jason Chewins, 45, described himself as a "gin convert" as he sipped a gin and tonic.

"I've just got into it in the last six months," Chewins says. "I like how it tastes refreshing."