Grantham was born in Camberwell, London, the son of Adelaide (née Flinders) and Walter William Grantham (1915–1998). He enlisted in the Royal Fusiliers regiment of the British Army in 1965, at the age of 18. See more

Having joined the Army (The Royal Fusiliers), as a teenager in the mid 1960s, Grantham was soon posted to West Germany, where he quickly found himself in debt to army colleagues. He resorted to criminal act… See more

On release from prison, Grantham decided to pursue an acting career and trained at the Webber Douglas Academy of Dramatic Art. His theatre work included a role in a play at the Battersea Free Theatre written by televisio… See more