The Doom Busters.

It's 1940 and war rages across Europe. Britain prepares for the coming invasion. But the war is a dull affair for Arthur Roundtree, a young man serving in the Home Guard. He dreams of action and adventure, but he remains stuck in a small, sleepy English village miles away from war due to a medical condition. However, when an extra-terrestrial creature crashes on the outskirts of the village, a training exercise suddenly turns into a deadly game of cat and mouse. Soon, Arthur and his companions realise they are fighting for their lives and to save the entire Galaxy!