Thanks to Dennis Nicholson for putting me onto this title.
The miniature special effects by Roy Kellino and Douglas Woolsey are pretty typical for British films made during the Second world War period. You get the sense that resources were much tighter than for their American counterparts. For one thing Britain was well into the war, materials would have been scarce while America still had another 2 years before entering the fray. The film would have been released around the time of the Battle of Britain.