The billboard picture dates back to 1962 and advertises the band as a support act to rock legend Little Richard.
Yesterday the find was hailed as a piece of “pure musical history” by experts who have valued it at £5,000.
At the time, Beatlemania had yet to sweep the country and group’s first single, Love Me Do, had been released only seven days earlier.
The poster, promoting a gig at New Brighton Tower Ballroom, near Liverpool, was discovered under wooden cladding on a platform wall by workmen refurbishing Bidston station on the Wirral.
It names the Beatles – whose hits included You’ve Got to Hide Your Love Away – in a “sensational line-up of top British rock groups”. The ticket price for the concert was 10 shillings and 6d – just over 50p in today’s money.
A total of 12 acts played at the five-and-a-half-hour gig. Among them was another Merseyside group called Lee Curtis and the All Stars whose drummer Pete Best played with the Beatles until he was replaced by Ringo Starr.
Merseyrail projects engineer Paul Collins said: “The contractors on site were ripping some boards off when they found the poster. They knew straight away that it was something important and needed to be saved.”
Doug Darroch, curator of the Merseybeat Story museum in New Brighton, said: “A finding like this is pure musical history. It’s significant because it shows how Brian Epstein, the band’s manager, was trying to push the Beatles. Part of that strategy was bringing in big stars like Little Richard and putting the Beatles on as the second biggest act.”
Bosses at Merseyrail are now trying to decide what do with the poster, but they insist it won’t be put up for sale, nor will it leave Merseyside.
Spokesman Andy Heath said: “We are considering displaying it at one of our city centre stations or lending it to a local museum.”
By Stephen Hayward