Martin Sheen says his son Charlie's battle with substance abuse is like having "cancer".

The 'West Wing' star admits it has been painful to watch the 45-year-old actor - who is currently receiving home rehab treatment for alcohol and drug use - implode in recent months, but he is prepared to support him because he believes addiction is a disease.

The 70-year-old screen icon - who has been in the UK to promote his new film 'The Way' - told Sky News: "He's an extraordinary man and he's doing well. We pray for him. If he had cancer how would you treat him? This disease of addiction is a form of cancer. You have to have an equal measure of concern and love."

Martin insists he and his wife Janet Templeton are prepared to help their son in any way they can as he attempts to get clean.

He added: "You realise we're not all on the same Journey all the time. We have to love that much more. We have to be that much more present."

The 'Apocalypse Now' actor strongly believes Charlie will overcome his demons and admits his dream is to star in another movie with his son when he is completely sober.

Martin - who appeared alongside Charlie in the 1987 film 'Wall Street' - said: "That would be another miracle and we'd look forward to it, very much so."

Charlie's behaviour in recent months has seen him indulge in drink and drug binges with numerous porn stars and trash a room at the Plaza Hotel in New York City in October following an alcohol and cocaine-fuelled evening with X-rated actress Capri Anderson.