A coop is where chickens are kept. A northerner pronounces cup as 'cup', not 'cap'. The Beatles sang as they did because they were influenced by Jerry Lee Lewis and Leadbelly and they, like numerous other English performers, used the 'voice' of their medium and unselfconsciously spoke scouse when not singing.

Billy Bragg, Neil Tennant, Morrissey, Noel Coward, used different forms of vernacular English to sing with, others like Gerry Rafferty use universal rock and roll. Who cares as long as it sounds good?