Pop legend Sir Paul McCartney is backing his younger brother against claims he groped a waitress at a party, calling the allegations "ludicrous".

Mike McCartney, 61, has been charged with sexual assault following the incident in a suburb of the brothers' native Liverpool, England.

But the former beatle, 63, is adamant his brother, "A devoted family man," is innocent.

He says, "Mike has respect for people and has earned respect for himself in his professional and private life."