In the beginning of the Forked Lightning episode, when Clegg first slips his bike chain and is being laughed at, you can hear one of the onlookers saying "Nice one, Cyril."
Clegg touches his cap in acknowledgement right after it's said. A small mistake but it grates me for some reason every time I hear it.
I also could not see any element of a mistake there. It was the catch-phrase for a very frequent commercial for Wonder Loaf sliced bread at the time.
Small mistake noted today in "Lipstick and Other Problems" - Marina on side of road with broken bicycle. Barry driving up in car with indicator already on to pull over to her long before he could have seen her.