Yes, disappointing on technical content. AFAIK digital speech codecs were a thing in 1980, and implementing a symmetrical block cipher on 2.4KHz would have bee

Yes, disappointing on technical content. AFAIK digital speech codecs were a thing in 1980, and implementing a symmetrical block cipher on 2.4KHz would have been possible using discrete logic or a processor like the Z80. Up to that point a different system was used, called a "scrambler". Speech was fed into a vocoder (parallel filter bank). The energy in each band would be used to resynthesise the speech using a reverse vocoder (noise/oscillator bank). In a scrambler the bands are shuffled before sending, and unshuffled at the other end. The result is speech-like, but incomprehensible. In terms of security this is no more complex than a simple transposition cipher. An adversary would have to record the conversation and then set about trying every band transposition. In practice you'd only have to get a few right for the speech to become intelligible once again, so the value was really to stop real time snooping and slow down an eavesdropper. The BBC article fails to communicate how the move to a digitised block cipher offered considerable security advantages over the incumbent systems.