From the outside, Boilermaker really looks like a dodgy electrics shop – complete with sullen salesman. But get through the door, past the muscle (he's the bouncer), and look for the door hiding behind the sink in the "staff room". Drinks are strong, the beer is cheap, and the house rules are fair.
The storefront of this speakeasy looks like an old barbershop, and you'll have to find the right book on the bookshelf to gain entry. There's complimentary popcorn and award-winning cocktails. Go for the Siam Saoco.
This elegant prohibition-influenced bar is tricky to find ("follow the hidden staircase to the doors emblazoned 'M'") but a worthy quest. If your preferred drink isn't on the menu, they'll happily make it for you.
This "Victorian botanical hideaway" has a secret behind its bookcase. You'll need to ask the staff for a key. If you can't get to Brum, then check out The Lost and Found's YouTube channel, where they walk you through their most popular cocktails.
The younger sibling of cult Bristol bar Hyde and Co, Milk Thistle offers four storeys of boozing. Press the doorbell of an unassuming townhouse, and cross your fingers that they let you in. You could also just book a table.
Yes, that is gin served in a miniature bathtub. The Gin Parlour at Jekyll and Hyde is tucked away upstairs, and really knows its stuff. Gin obsessives can even partake of a gin and food fusion menu. If gin's not your thing, the cocktails downstairs are pretty good too.
Ernest is easy to find, once you know what you're looking for. Tucked away under a bridge, by the Biscuit Factory, Ernest is a cosy café and bar, open all hours. "Relaxed during the day and lively at night" aka ideal.
If you're looking for something a little more unique, keep an eye out for Boiler Shop Steamer, a monthly food, drink, music, and art event, held in the Boiler Shop (behind Central Station).
Bristol's best-kept secret. And for good reason: You can only reach this riverside haven by boat (or by a hidden private path, if you're very determined). Once you dock, you can indulge in a cream tea, or sit on the deck with a cold glass of wine and watch the river flow by. Beese's is open Easter to September yearly.
Located in a former public toilet, this Kentish Town bar only opened in January 2015, but it's already made a name for itself. They often run caption competitions for their sign, too, so keep your thinking hat on.
Not "hidden", strictly speaking, but this local favourite has one of the best secret beer gardens in the city. The garden is a suntrap in the summer, and has heaters when it gets a bit nippy. Plus, the hot dogs are boss.
If you'd prefer a different kind of Glasgow dive bar, then try the Flying Duck. Kitted out like "your gran's house", their kitchen is all-vegan, and they serve a cocktail called the Sailor Buck (Buckfast, Sailor Jerry, and Coke).
A hidden gem in Cardiff, this unassuming and tucked-away bar (near the Motorpoint arena) has a fantastic selection of craft beers, and really punches above its weight. If you're keen, they also have a pub theatre attached.
A compact parlour bar, down some treacherous Soho steps, B&H's drinks are potent and delicious, and often served in their signature teacups. They also have two other locations (Clerkenwell and Goodge St).