The Get Carter star was evacuated from London during World War II in the late 1930s, and was sent to live in Berkshire, England, along with another boy.
The woman who was paid to take care of the pair made them live in squalor, and Caine recalls being covered in painful sores as a result.
He was rescued by his mother Ellen who sensed something was wrong - but the mercy mission almost ended in disaster when she punched her son's carer.
The actor says, "I was locked in a dark cupboard under the stairs while they went out. My mum came to get me - she had a sixth sense that something was wrong - and she whacked (hit) the woman, just hit her in the face.
"Someone called the police and she nearly went to prison. My mother was like a boxer and she was really tough. She was hysterical when she saw the pair of us, because we were covered in sores."