Section 30A of the 1988 Copyright act states that a "parody" is something that imitates a work for humorous or satirical effect, a "pastiche" is a composition that is made up of selections from various sources or one that imitates the style of another artist or period, and that a "caricature" is something that portrays its subject in a simplified or exaggerated way, whether insulting or complimentary and whether for a political purpose or solely for entertainment.
So, it's a pastiche of The Wicker Man and Trumpton/Camberwick Green. Case closed.
Personally, I thought it was brilliant, and if anything could foster a mild revival of the old series if they cared to capitalise on it.
Given that it's "the family of Gordon Murray", and not Gordon Murray himself, methinks the 95 year old is prossibly non-compos mentis enough to bitch about it, or safely tucked away in a home where he won't be bothered by such trivialities as the real world.
Either that, or their legal dept said "you'll lose the case overall, but best rattle our sabres to show we're defending our IPR so we mitigate risk later on", which I know applies to trademarks and not copyright, but who knows what they've registered.