Many Thanks, I've added a comment to the Lusitania website.
His name is Frederick James Kerslake. Possibly born Sept 1878, but not certain. Married Q2 1904 in Tynemouth, Northumberland to Ada Emily Smith and I've sent off for the marriage certificate to gain more info. Had one daughter Beatrice May, born 19th March 1905 in Tynemouth.
Frederick and Ada also had a son Sydney James who died aged 2. Think Sydney was born March 1909 in South Shields and think he died Sept 1911, death registered in Doncaster. Ada, Emily and Sydney were on the 1911 census in South Shields, but no Frederick (although he could have been at sea).
Frederick's father may also have been called Frederick and his mother Frances, but I'm not certain.
Has obviously crossed my mind the story was made up and he ran off. Have also considered he did crew on the Lusitania to New York but didn't come back for some reason.