One serious contender for this title is the Railway Hotel in West Hampstead. During the 1960's it ran a weekly club night known as Klooks Kleek.
Originally a jazz club, the music changed to reflect the new interest in Rhythm and Blues. West and South West London were UK blues centres in the early '60's, and a number of small venues became part of a thriving new club scene including the Marquee, the Flamingo, the Ricky Tick, and the Crawdaddy. Klooks was small upstairs function room. Unlike other venues it had no stage at all. There were no mixing desks, lighting rigs, or sound checks; the bands just tuned up and played. While the Graham Bond Organisation was probably the most respected band of that era, others went on to much more success, among them the Rolling Stones, The Yardbirds, The Animals, Eric Clapton, Family, The Who, Rod Stewart, Cream, Jethro Tull, Led Zeppelin all of whom played at Klooks. There was also Zoot Money’s Big Roll Band, Chris Farlowe and the Thunderbirds, Georgie Fame, Herbie Goins and the Nightimers, Geno Washington and the Ram-Jam band, Cliff Bennett and the Rebel Rousers. Occasionally, American bluesmen would drop in -Howlin' Wolf was there, and Jimi Hendrix jammed with John Mayall.
By the late '60's, the scene had moved on, and the venue was renamed the Moonlight Club with bands like Siouxsie And The Banshees, The Cure, The Jam, Joy Division, and The Stone Roses playing gigs there early in their careers.
The Railway still features some live music on Friday and Saturday nights.
The Railway, West Hampstead , 100, West End Lane, NW6 2LU