The British Film Institute website - and you can watch the film for free there if you click on the still above - describes The Heart Within thus:
Teenager Danny lives in London's docklands and befriends Victor, a Trinidadian dock worker, who becomes the chief suspect in a murder in this low budget crime thriller which cleverly mixes Boy's Own adventure with social realism. It gives postwar Britain's most prominent black actor, Earl Cameron, one of his best screen roles as a man on the run for a crime he didn't commit.
This is a departure from other 1950s British films which located black characters in colonial Africa and viewed them as 'problems' or 'exotics'. The Kings of the Caribbean provide some great calypso music.Notable too are the London locations, which clearly show the effects of wartime bombing.
Earl Cameron is still with us at the age of 99.
Danny is played by a young David Hemmings. At one point, where he has been told off by a policeman and is sprawled out sulking, his body language is exactly the same as in Blow-Up a decade late.