Chocky by John Wyndham. 80s, I think. I re-watched it recently on YouTube (along with its two sequel serials, not by JW but "based on characters written by JW") also 80s.
The Changes by Peter Dickinson.
Both children's TV serials, both scifi/post-apocalyptic/AU. They don't make children's serials like they did in the 80s. They don't make adult TV serials as good as the children's serials of the 80s when it comes to plot and so on. Yes, special effects have come on leaps and bounds. Sadly, special effects do not make up for a lack of gripping plot and characterisation.
Then again, many great series are started in the US and then cancelled before they are allowed to get even better, e.g. Carnivale, Dollhouse, Firefly,…
Just my 2¢.