The actor Sandy Ratcliff, who has died aged 70, touched the hearts of millions when she appeared in the original cast of EastEnders as Sue Osman, whose son Hassan died of cot death in the summer of 1985, just months after the television soap was launched. It was one of the early dramas to beset the fictional Albert Square as the BBC took on ITV’s Coronation Street in the battle of the soap ratings.

Sue ran the Bridge Street cafe in Walford – speaking her mind and getting into rows with customers – and had little help from her minicab-driver husband, Ali (Nejdet Salih). Her grief over losing their son dominated much of Ratcliff’s four years in the serial. Experiencing a phantom pregnancy as she longed for another child, dealing with Ali’s gambling, neglecting him after giving birth to another son, Little Ali, and wrongly believing she had cancer on finding a lump in her breast led to a deterioration in her mental health. Eventually, in 1989, Sue was sectioned and put in a home.

However, her screen character’s tragic life almost paled into insignificance when compared with the actor’s own troubles. “When I was about 10, my school sent me to the Tavistock Clinic,” said Ratcliff, who was born in Islington, north London, to an insurance seller and his wife. “I was a grade-A student who was also trouble – a bit rebellious.” Two years later, she was expelled from her local grammar school and she was smoking cannabis aged 14.

Later, she became a bass guitarist in the rock bands Tropical Appetite and Escalator, a disc jockey and a photographer’s stylist, before being put in front of the camera as a model. Lord (Tony) Snowdon tipped her to be one of five Faces for the Seventies in the Sunday Times magazine in 1972, and she acted in a couple of BBC schools programmes.

Sandy Ratcliff, right, with Grace Cave in Family Life, 1971, directed by Ken Loach. Photograph: EMI/Sportsphoto/Allstar

Her break came when the director Ken Loach cast her as the lead character in his 1971 film Family Life, a remake of his 1967 TV play In Two Minds, written by David Mercer. It challenged the traditional view that people with schizophrenia were born with the condition and could be cured in the manner of a disease – with treatment that included electric shocks. Ratcliff played Janice, whose mental ill health was caused by her mother’s domineering, repressive nature, in the view of a new wave of psychiatrists led by RD Laing.

The actor’s rebellious streak as a child made her ideal for the role and Loach made her live it throughout filming, forbidding her from washing her hair and wearing makeup. She later said that making the film helped to turn her life around and made her think about mental health issues.

However, she had mixed feelings about the whole experience once she left the cameras behind. “I took Jan home with me a little bit and found it really hard,” Ratcliff told me in 2003. “I wanted her to be stronger because she wasn’t schizophrenic, just a scapegoat, a victim of the family. It upset me. When filming was over, I felt abandoned and got quite depressed for a while. Then, for a couple of months when the film came out, I was being invited to every party going, but I wasn’t working most of that time and there were times when I didn’t have the bus fare to get to places I was supposed to be going.”

Nevertheless, she gradually built up a CV of small roles on television before landing the part of Sue in EastEnders. She popped up in popular dramas such as Hazell (1978), Danger UXB (1979), Shoestring (1979), The Gentle Touch (1980) and Minder (1982).

In 1974, she had a short run in the soap Crossroads as Barbara Wells, who went out with the village postman and motel bartender, Vince Parker, while also being engaged to, and eventually marrying, his father, George.

Ratcliff’s off-screen troubles continued to haunt her, though. Before joining EastEnders, she became a heroin addict and, in 1983, was jailed for conspiring to supply cannabis, serving eight months in Holloway prison. Fame as a soap star brought newspaper revelations about Ratcliff’s past and she offered to quit the role, but the producer, Julia Smith, stood by her.

The headlines kept coming after she did finally leave. Then, in 1991, she gave an alibi in court to a lover of 10 days, Michael Shorey, when an Old Bailey jury found him guilty of murdering two women. She said he and she were making love at the time the crimes were said to have been committed, later adding that the police must have “got their timings wrong”.

Her final television roles were in Maigret in 1992, as a burglar’s wife, and Rona Munro’s drama Men of the Month two years later. She then stepped out of the spotlight, suffered several nervous breakdowns, beat her drug addiction, trained as a counsellor and drove London ambulances.

Ratcliff had suffered three strokes in the past five years and was then diagnosed with cancer, leading to her leaving her north London flat to live in nearby sheltered accommodation.

Ratcliff’s 1968 marriage to the photographer Peter Wright ended in divorce. She is survived by her son, William, from a relationship with the theatre director Terence Palmer.

• Sandy Ratcliff (Alexandra Ratcliff), actor, born 2 October 1948; found dead on 7 April 2019