Works - if you look past the cracks
It's amazing isn't it? Where did the Beeb dig this up from? Makes you wonder what else there is in their vaults. I thought I'd seen just about everything of this genre and era, but it's gratifying that small treasures such as this can come to light.
Granted, it's creaky in places and 'of its time' in certain aspects (the age of the lead man is of an era when such roles were prevailingly filled by actors of 40-55 years viz. Bogey, Cooper, et al, and seems very reasonable now that I'm of that maturity myself! Mind you, I can see why he was called 'the king of the 'B' movies'), but the storyline was compelling and some of the dialogue worthy and insightful. The encounter between Reed and the female sculptor was of particular merit and had the weight befitting a two-hander play by an angry young playwright of the time.
I agree, it was reminiscent of 'A Clockwork Orange' and in some ways, the cultish 'Wicker Man' (coastal location and denouement), and, of course,'The Children of the Damned,' and doubtless a few others. I also concur with another poster in that they should have made the kids more sinister. This would have been possible and to still retain their essential-to-the-plot innocence.
A very significant record too, of that era of nuclear tension; especially so for myself as someone who attended CND marches in his pushchair at about that time.