Jazz in the UK - like jazz everywhere else - has gone through several phases. It's hard to itemise these - there are always musicians who straddle the phases (Stan Tracey for example); there are always musicians who play completely different music to what most are playing in a particular phases; and there's plenty of scope to argue over what the phases actually are!
But working off my interpretation of when UK jazz hit particular points of popularity or activity I'd suggest the following:
1. The Dance Band Days - i.e pre-50s
2. The Bebop influenced period when the likes of Tubby Hayes and Ronnie Scott first appeared.
(Apologies for oversimplifying the first 30 years but I'm not very familiar with those times)
3. The Trad Boom - late 50s/early 60s when jazz almost became pop music again, though in a very restricted, Dixielan imitation. The huge impact of this time can be seen at any UK Flower Show or County Fair where you're bound to get a 'Jazz Band' playing "And When the Saints..."
4. The 60s crossover period - Mike Garrick, Ian Carr, John Surman, Mike Westbrook heading for a more personal style of UK jazz, less dependent on the US model; also the period when the free improv scene took off - John Stevens et al.
5. Late 60s/70s - a period where both free jazz and fusion kicked in; and the point where the music of the Blue Notes (mentioned in SEK's post - they're influence was huge) really started to colour much of the newer music. What I like to think of as the 'Ogun' era (and when I got interested) - Keith Tippett, Harry Miller, Mike Osborne etc.
6. The mid-80s - jazz briefly became trendy again and people like Courtney Pine, Andy Sheppard, The Jazz Warriors, Loose Tubes had their moment in the sun (the latter two groups have spawned much of the front rank of the contemporary UK scene).
7. The 90s until now - In my view UK jazz went through a bit of a trough in the 90s. Lots of great musicians but few chances to record and a tendency for the scene to be dominated by musicians from the earlier eras working within their comfort zones (Andy Shepherd, Tommy Smith, Guy Barker - all excellent musicians who've done much for the music; but...).
However, something is stirring! I read alot about a collective in London called 'Fire' who are producing all manner of groups (several to be showcased at the Cheltenham Festival in May); and musicians from the ethnic communities like Nikki Yeoh and Jason Yarde are doing interesting things. There's also something of a Scottish Renaissance with the likes of Trio AAB (mentioned above) and Brian Kellock. An exciting time.
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I post this simply because most of the posts so far dwell on UK jazz in the past. It's still very much a vibrant scene. The Tea Party goes on!
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The posts unwittingly suggest Westbrook as a musician whose first three recordings mark his most significant work. Far from it - he's still very active today with a major piece premiered last year.
To my mind the heart of Westbrook's music lies in the 70s and 80s - 'Metropolis', 'Citadel Room 615', 'Goose Sauce', 'The Westbrook Blake' and, above all, 'The Cortege.' I find the latter to be the most successful extended jazz recording I've heard (from any country!). Now there's a claim!