Courtesy of EuroLondon Films Ltd

In retrospect, it seems surprising that, after a decade of landmark political television films, the director/producer partnership of Ken Loach and Tony Garnett should choose the year Margaret Thatcher came to power to release a children's adventure film. Garnett later wondered whether the film's real motivation was a desire to achieve a cinema release after years of struggle, taking advantage of the National Film Finance Corporation's funding opportunities for children's films.

Loach's adaptation of Leon Garfield's 1968 novel changed the title character to a Frenchman, played by Jean Franval - in a bid for French co-production funding - and moved the story from Surrey to North and East Yorkshire, for their unspoiled landscapes. Some of the cast came from South Yorkshire, because Loach found the dialect simultaneously contemporary and historical: he re-used some actors from his earlier 'The Price of Coal' (Play for Today, BBC, 1977) and drew child leads Stephen Hirst and Louise Cooper from Barnsley schools (Cooper from the former school of David Bradley from Kes, 1969).

The film was handicapped by financial problems. Shot in just six weeks in summer 1978, it had a still more rushed post-production schedule, and Loach long wanted to re-cut a film he considered "one that got away". He eventually presented a shorter director's cut on the 2010 DVD release.

Despite its problems, Black Jack is a charming, underrated film. It shares the concern of other Loach films for young people failed by their elders and abandoned by society, and while the historical attitudes to mental illness that it presents jar with those in 'In Two Minds' (The Wednesday Play, BBC, 1967) and Family Life (1971), Belle's recovery after leaving bourgeois family constraints echoes those productions' perspectives.

It's also an accomplished historical film, which sought to avoid other films' anachronistic clichés through Loach's characteristic techniques, Martin Johnson's design, and unconventional music - Bob Pegg's score and in-scene performers such as Packie Byrne - which prioritises the people's popular music. Chris Menges' photography, meanwhile, favoured the textures of old photographs and paintings: exteriors were shot on grainier Super 16mm, with interiors - some painterly, some almost under-exposed - on 35mm with low natural light and candlelight.

Loach planned a follow-up children's series, Garfield's Apprentices, for Southern TV, but couldn't attract the necessary international co-producers. Garnett later criticised his own contribution to a film he "should never really have done". This would be Loach and Garnett's final collaboration.

Dave Rolinson

Click titles to see or read more