Data broadcasting companies did use scanlines originally intended for Teletext/Ceefax in the 90s to transmit public information (e.g. weather forecasts, water levels): https://en.wikipedia.org/wiki/Datacasting
In that case the "antenna in" signal did go to an ISA decoder card in the PC, but it appears that the BBC Micro also had an adapter for receiving classic Ceefax pages, some of which also contained software: https://www.teletext.mb21.co.uk/gallery/ceefax/telesoftware/
In that case the "antenna in" signal did go to an ISA decoder card in the PC, but it appears that the BBC Micro also had an adapter for receiving classic Ceefax pages, some of which also contained software: https://www.teletext.mb21.co.uk/gallery/ceefax/telesoftware/