Roman Abramovich is understood to be building a secret £20m music venue beneath Chelsea FC’s stadium

According to a source close to the project, the 500-capacity venue is due for completion in November or early December, and is located underneath the East Stand of Chelsea’s Stamford Bridge stadium.

The main contractor on the scheme is Essex-based interiors specialist Cumberland.

The source said the venue would offer a performance space for bands, but was likely to be used for “Abramovich’s VIP friends” rather than being open to the public.

They added that the Russian billionaire might rent it out as a nightclub for private parties. They said: “It’s quite an intimate space because it’s in a basement, but it will be able to hold about 400 to 500 guests.”

The centrepiece of the space, which will have what the source called “a gritty industrial design motif”, is a 4m waterfall that will greet guests when they enter and descend the staircase at the entrance.

The stage will be a hydraulic platform that can be raised and lowered during performances. It is understood that Abramovich got the idea for this after seeing one in a club in America.

The club will incorporate private booths for customers, each with their own personal television screen, and a green room where bands can relax before going on stage.

The music venue is on the site of Stamford Bridge’s former Purple nightclub, which was one of London’s most upmarket clubs before it closed in 2003.

Abramovich is no stranger to grandiose, yet clandestine, entertainment projects. Last year he secretly paid the Hamburg shipbuilder Blohm + Voss £288m for a 170m yacht-cum-frigate that was fitted with a cinema, sports complex and disco - as well as a mini-submarine, guided missiles and two helipads.

Chelsea FC plc, the Abramovich vehicle that owns the football team, as well as Stamford Bridge’s hotels, health club and convention centre, was unavailable for comment.