The UK was setting up an academic network (SERCNET) in the late 1970s. In 1983, the Joint Academic Network (JANET) was set up, incorporating SERCNET. The protocols used on this network were "open" in the sense that specifications were published, in the UK Coloured Books, and vendors were expected to provide compliant applications. This gave the UK a good start in networking. The plan was that the interim Coloured Books protocols would be used until the ISO protocols had been worked out, ratified and implemented, and then JANET would migrate to those. While this plan was slowly grinding away, though, the ARPANET became the Internet, and large amounts of friendly IP-based software were becoming available, leaving the UK academic community at a considerable disadvantage.
Finally, the JANET network was persuaded to institute a pilot IP service (popularly known as Shoestring), which became a production service (the JANET IP Service or JIPS). Initially, IP was carried over the existing X25 network. By mid 1994, IP traffic accounted for considerably more than half of the traffic on the JANET network.
The recent additions to the network are called SuperJIPS, which operates native IP at multi megabit per second rates, and indeed the plan is to phase out the X25 links, and to carry the remaining X25 traffic over the IP network by an encapsulation technique.
To summarise, then, the JANET IP service (together with all of the connected campus IP networks) is now a proper part of the global IP Internet.