Quite a tough little film with a particularly nasty, vindictive ex-employee sabotaging a firm's lorries after being sacked for persistently smoking near petrol outlets. He then falls in with a bunch of crooks with much more ambitious aims.
The "hero" is a youngster with an aptitude for repairing...anything! He and his spirited sister save the day, with help from other kids, adults (including the lady at the local "caff") and the police getting into the action late in the day, with an extended chase and fight sequence that just about avoids Keystone Cops comparisons.
Another valuable snippet of post-War life. This was part of Rank's short-lived Children's Entertainment Films series; the Children's Film Foundation series started soon after.
Thanks to UK's Talking Pictures channel for giving this a showing.