UCL was on both the JAnet X.25 network and the Internet when I joined in 1985, and provided a relay service between the two for email and for telnet. Maybe others - not sure. Relaying email required translating the address order as the UK used big-endian "foo@uk.ac.ucl.cs" and the rest of the world used little-endian "foo@cs.ucl.ac.uk". There were a whole set of heuristics to figure out which order the destination should be, which worked fine up until Czechoslovakia joined with their .cs domain. I think it was probably in the early 90s when JAnet fully deployed IP-over-X.25, and all UK universities became IP-reachable, but some would have been reachable before then.
Peter was also responsible for the UK using .uk instead of the ISO country code "gb" which it should have been according to "the rules". But Peter insisted on .uk, as the official name of the country was "The United Kingdom of Great Britain and Northern Ireland", and he thought GB was not properly inclusive of Northern Ireland. It took until 2021 for UK to replace GB on car number plates (and stickers for travelling abroad).
Peter was also responsible for the UK using .uk instead of the ISO country code "gb" which it should have been according to "the rules". But Peter insisted on .uk, as the official name of the country was "The United Kingdom of Great Britain and Northern Ireland", and he thought GB was not properly inclusive of Northern Ireland. It took until 2021 for UK to replace GB on car number plates (and stickers for travelling abroad).