" `Let Him Have It' " is another fascinating fact-based British film from director Peter Medak, whose "The Krays" last year was a very violent exploration of real-life gangsters terrorizing London in the '60s.

This new film also has to do with young London gangsters, this time in the '50s, but takes a decidedly different approach and is not nearly so violent.

The story hinges on the title phrase — when two teenage hoods were confronted by a policeman and one of them yelled to his wild-eyed, gun-wielding companion, "Let Him Have It!" But did he mean, "Give your gun to the policeman!" or did he mean, "Shoot him!"?

The question of this statement's intent doesn't really come into play until the film's final quarter during a courtroom sequence. But Medak has a point of view. He's convinced — as many people in England apparently are — that young, slightly retarded and epileptic Derek Bently was railroaded by British justice.

The film is Derek's story, and the first 90 minutes explore his life to show how he came to be in the position that led to this confrontation. It opens with the aftermath of a bombing raid over London in 1941, as poor young Derek is pulled out of the rubble of a destroyed building, which apparently caused him some brain damage.

The next scene, several years later, shows him having fallen in with a group of young ruffians who commit vandalism. Derek is along for the ride, but, of course, is the only one caught and winds up in a reform school. Eventually, Derek (played throughout the bulk of the film by Chris Eccleston) is released and spends the next year at home in his parents' custody. During that year he refuses to leave the house — and often doesn't leave his room.

Finally, his loving sister Iris (Clare Holman) coaxes him out and Derek gradually develops

MOVIE the necessary confidence to start going out into the world on his own. He even gets a job sweeping streets.

For reasons never adequately explained, a younger hoodlum, Chris Craig (Paul Reynolds) latches onto Derek and lures him into a life of petty crime. Chris' older brother is a high-rolling gangster and, emulating him, Chris collects and trades handguns, always carrying a loaded pistol on his person.

Though Derek is concerned about their activities and realizes his overprotective parents (Tom Courtenay, Eileen Atkins) disapprove, he is seduced by the attentions of Chris, who is essentially his only friend.

Chris is such a loose cannon that it's apparent to the audience, if not to Derek, that sooner or later someone is going to be killed. But in the film's approach, Derek is strictly an innocent victim in the wrong place at the wrong time. And so, eventually, Chris kills a policeman as Derek helplessly watches.

Much more shocking, however, is the trial of Chris and Derek as the film winds down. Both are charged with murder, despite Derek's only being an accomplice. The instructions of the judge (Michael Gough, who plays Alfred the butler in the "Batman" movies), the meekness of the defense attorney, the finger-pointing of police — all serve to get the strictest convictions for both boys. But because Chris is only 16 and Derek is over 18, Derek gets the worst of it.

Derek Bently's case has been celebrated in England for 40 years, and the film has apparently stirred up the controversy again. The first-time screenplay, by Neal Purvis and Robert Wade, is very good, and the performances are excellent all around, with kudos to Holman, Courtenay and especially Eccleston, who manages to make Derek dignified but unsentimental. Less successful is Reynolds who plays Chris like a James Cagney caricature and lacks charisma.

Most of the way Medak's direction is sensitive and compelling, but the ending seems protracted and at two full hours, the film could stand some trimming.

Still, a very touching story, " `Let Him Have It' " is a successful look at a miscarriage of justice, as well as a family's love and devotion.

It is rated R for violence, which is restrained, and profanity.