Owners-brothers Max and Noel Venning and their team conjure up elegant, beautifully balanced, carefully crafted cocktails. The standout is the Dirty Martini at £13 ($16.50), made with olive oil-washed vodka (which adds luxurious smoothness), vermouth with fragrant Ethiopian kosoret and an indispensable pinch of sea salt to amplify the drink’s savory side.

This is a modernist cocktail bar is like Willy Wonka's boozy laboratory. The Unfiltered Martini features a tincture made from Maris Piper potatoes. Steamed, injected with acidophilus microbes and briefly fermented, the humble spud takes on a remarkable flavor of vanilla ice cream. Mixed with wheat-based Boatyard vodka, it is given a short stir over ice and garnished not with an olive but with a citrusy, boba-like little globe for a light, tropical finish.

This bar at the Japanese grill and sushi bar Nijū is a chic Mayfair hideout whose bartenders are inspired by the seasons. The Ramson (wild garlic) Martini (£19), for instance, is a truffle-scented variant of the dirty martini. The off-menu classic Forest Martini (available year-round, at £21), is like a boozy gulp of woodland air; it takes Botanist gin from the whisky-obsessed island of Islay and spikes it with a distillate of pine and moss.

Located in the St. Pancras Renaissance Hotel, Gothic’s velvet-draped room with soaring ceilings and riotously rococo décor is the perfect backdrop for a bespoke cocktail. The signature Eau de Martini (£17) lets you customize your tipple with a choice of Hepple Gin from Northumberland or X Muse barley vodka from Scotland; a house-crafted blend of vermouths;and a dash of one of five eaux de vie—herb or stone fruit, perhaps—for an aromatic flourish inclined toward the fragrant side of dirty.

At the clubby, cozy space beside Clare Smyth's renowned Core restaurant in Notting Hill, bar manager Vincenzo Ciaccio’s bracingly sour Gin & Pickle (£21) is an especially aromatic version of a dirty martini. Ciaccio makes it with Sapling London Dry gin, tangy Champagne vinegar, a smoky, medicinal hint of black cardamom and pickle juice.

Located on the fourth floor of the National Portrait Gallery, Irish chef-restaurateur Richard Corrigan’s Portrait restaurant and bar is an oasis for footsore culture hounds. The star of the show, and a perfect partner for a platter of Irish oysters, is the Salt & Vinegar Martini (£14), a heady concoction of Sapling Gin, Noilly Prat vermouth, a little pickled onion and a dirty dash of pickle juice.