What TV show had the highest ever British viewing figures?

Easy, eh? The Royal Wedding. Or the Morecambe and Wise ’78 Christmas special. Or England-Germany in 1996. Or Den and Angie, Christmas ’86. Or. Or.

It seemed like an obvious pub quiz question. It is an obvious pub quiz question. It’s just we can’t find the answer to it. We can find lists for each year back to 1992. We can find conflicting figures for all of the above. We can find controversy over how the figures are measured and dark mutterings that earlier figures need to be down-weighted. But we can’t find a simple, authoritative top ten listing. The Internet, pfft.