Unlike what happened with Doctor Who’s early years, Blue Peter apparently took great lengths to preserve their broadcast history. One reason several clips from lost Who episodes survived is they were used on Blue Peter.

U-Matic began life as a home video format that was too expensive for most people in the early '70’s. An early Sony U-matic home deck appears as a rich man’s toy in a Columbo episode as a plot device. It was still cheaper than most broadcast gear, and Sony refocused it’s efforts. It was firmly the format for colleges, small tv stations and other institutions by the 1980’s. Betacam was way too expensive for the college I went to. We received programming as an affiliate of National College Television on U-Matic tapes until direct satellite delivery took over in the 90’s.

I take great exception to your characterization of Betamax having used it many times over the years. U-matic was never more to me than a major pain in the ass back in college. The decks broke down so often you could set your watch by them.