All has been revealed!
Birth/death certs show that Percy George WEST Peck was born in 1888, 3 years' before his parents' marriage. Although shown as West on the census' , he married as a Peck and died in 1921 as a Peck (from pleurisy, pneumonia and bronchitis).
So the motorcycle story was a case of Chinese Whispers because it was his cousin, Roland, who died in the accident.
However, I still can't find any trace of him in the military records as either a Peck or a West?