MAY CONTAIN SPOILERS
I remember this being on late on ITV in the early 80's when I was a nipper, and they showed decent movies in the small hours, instead of non stop bingo, or mind numbing quiz shows.
It stars Forrest Tucker, who regularily appeared as heavies or weathered heroes in American westerns and thrillers. He also appeared in Hammer's adaption of Nigel Kneale's 'The Creature' and The Trollenburg Terror, both classic British Sci-Fi, around this time.
The plot concerns experiments in matter transference that lead to flora and fauna being exposed to radiation rays, creating insects of monsterous size. Most of these are just real insects made to appear larger, but it is very effective. There is also a benevolent visitor from another planet, who comes to warn the scientists to discontinue their experiments, and also to sample the bitter in the local pub, which he eyes up suspiciously. In fact, a lot of the action takes place in the Local, with scientists, the military, villagers and the odd alien discussing the impending fate of Planet Earth over a pint.
A charming film, with a serious message, that overcomes its limitation of budget, with its obvious enthusiasm.