All the external shots of the village show the correct type of terrace housing but many clearly have modern UPC type windows and doors which didn't exist as early as 1966.
Though the action is set in October, 1966, in one scene (5:54 minutes in) the green Rover P6 in the foreground in Aberfan is a Series II model not launched until 1970. The plastic grille is the most obvious giveaway.
When Wilson's last audience of the episode with the Queen ends, Elizabeth does not ring the bell to alert the people outside to come and open the door.
In audience with the queen, right after arriving from Aberfan, the PM sits with legs crossed whose feet point to her. A gentleman never points his feet towards anyone ... specially to his Queen.