Campaigners fighting to save Kensington Odeon say developers knocking down the building have inadvertently discovered original interior assumed to be long lost.
Original plaster details of the 1926 Art Deco building have been exposed, with campaigners now calling for an immediate halt on further demolition work.
Historic England, which refused to list the building following the issuing of a Certificate of Immunity in 2013, has been formally notified to re-inspect by the campaign group Friends of the Kensington Odeon.
Guy Oliver, from Friends, said: “This should be a game changer.
"These are the details we were told were missing and why it couldn’t be listed in the first place.
“This should change that decision.”
The Certificate of Immunity stated original details did not exist under later shop fittings including the vaulted ceiling, dress circle, Proscenium arch with its masks and details, Tea Rooms and reception area.
However, campaigners say the discovery of these treasures prove the certificate was issued erroneously and have sent a letter to Historic England head, Duncan Wilson.
There was anger when the organisation failed to list the building, leading to thousands signing a petition opposing the demolition of the building, whose customers over the years have included Princess Diana, Alfred Hitchcock and a young Benedict Cumberbatch.
The Sherlock star is one of the signataries on the petition, with other notable names including guitarists Jimmy Page and Brian May, actors Kristin Scott-Thomas and Sir Ian McKellen, and director and writer Richard Curtis.
Campaigners say the building houses architectural gems such as a marble staircase and mosaic floor in the foyer and that the cinema, which has hosted countless premieres over the years, and is an integral part in British entertainment history.
Following the discovery of the original interior a joint statement put out with the Cinema Theatre Association and Friends of the Kensington Odeon said: “This is an international heritage asset and key cultural centre for London, hosting many premieres with Britain and Hollywood’s finest beamed around the world.
“The impressive exterior entrance and the pair of sweeping, marble staircases ascending up to the theatrical auditorium of this cinematic, architectural masterpiece used by celebrities such as Reece Witherspoon, Johnny Depp, Madonna , Kate Winslet, Alan Rickman, James Page and many others.
“Further demolition needs to be stopped, these images prove that a precious survival of our cinema history is being destroyed at this moment.”
Mr Oliver said: “We want a English Heritage inspector to go down and look at the building in its entirety and list the front part of the building in its entirety.
“At the moment the developers only have to keep part of the facade but we believe there is enough evidence to now reconsider.”
The real estate investment and advisory company Delancey is developing the cinema site.
Under plans for the building which have been given approval, a new seven-screen cinema will be built.
The development, which would see the parts of the Odeon’s facade retained, would include luxury homes, a cafe, bar and restaurant.
The Friends hope to open an arts centre called The Hitchcock, Kensington.
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