Let's focus first of all on dual-line flying, and let's consider a team as consisting of three or more flyers. Within the UK, I'm only aware of little more than half a dozen active dual-line teams. First of all, of course, the reigning world champions, the Scratch Bunnies. Then we have the reigning UK champions, Team Flame, and the current UK runners-up, Airheads. Besides these three, undoubtedly the UK top, I know of Sky Symphony, Pallas Family Flyers, and Flying Colours (are they still active?). Then there is L-katz, of course. And let's not forget The Flying Squad; they are first and foremost a quad-flying team, but occasionally also fly dual-line kites. So that's eight active teams in all.
Moving on to dual-line pairs, I know of Evolver, consisting of Carl and James Robertshaw, part of Scratch Bunnies. Ex-Grads consist of Keith and Vee Griffiths, part of Airheads. Phoenix is made up of Fran Burstall and Tony Shiggins, part of Team Flame. Allan and Marilyn Pothecary fly as Close Encounters. Team Spectrum is formed by Bryan and Carl Wright. David and Angela Green don't really have a festival name, but sometimes call themselves 'The Greenies'. And then we have Flying Fish and Wings on Strings, both part of L-katz. So eight active dual-line pairs that I'm aware of in the UK.
Briefly crossing over to quad-line teams, I know of The Flying Squad, Decorators, Fusion, Team4Mation, Haven Flyers, and Snuff.
Eight dual-line teams, eight dual-line pairs (some of which are part of a team) and half a dozen quad-line teams. That's how rare pair/team-flying is in the UK. We're not extinct (yet), but there sure ain't many of us ....
Of course, I can only list pairs and teams that I'm aware of, and that's mostly because they compete and/or display at kite festivals. If there are any active UK-based pairs or teams that I've missed above, please let me know and I'll update.