The previous reviews are being unfair - yes the sound quality has some flaws but it is very listenable - certainly not like a dodgy bootleg. The audio quality itself is actually quite good, the main problem is with the balance. The accompanying booklet explains all this & the context at great length. There is an essay by Dave Gelly, who is not only a respected critic but was playing sax at the concert on the night! There is also a detailed note from the tape restorer Martin Mitchell. The historic context is that key members of the Ardley big band had formed a rock group - Coliseum - who were enjoying great popular success at the time. The NJO & Coliseum "united" for a short tour & this Camden gig is the only recorded evidence of the auspicious occasion. Recording a big band (20 or so musicians) is always difficult at the best of times - this recording seems to have been a two track tape made impromptu off the mixing desk, with certain instruments (& vocals) low in the mix. And then, as per usual, the tape has been left in bad storage for decades & needed to be salvaged, cleaned up & restored. No, it doesn't sound like an ECM record (thankfully!) but it's a good document of the band on the night.
As for the previous reviewers' other complaint about live recordings like this being released when many classic Britjazz LPs remain unreissued, that is because big record companies don't release jazz back-catalogue they think won't make money & yet, as is well known, often refuse to license it to smaller specialist labels for reissue. It is shameful but hardly the fault of small archival jazz labels (who I'm sure would love to reissue the classics) & all the more reason why specialist labels should be encouraged to release any decent tapes that unexpectedly turn up.
Someone who is really picky about sound should maybe get "official" professional multi-track recordings such as Mike Gibbs big band live double "Just Ahead" or Collier's live albums (eg Mosaic) or the "Will Power" live double (which featured an Ardley track). But I think most fans who love the classic era of British modern Jazz will welcome the chance to hear a rare vintage concert like Camden 70 with its amazing band line up & set list. (important note: the music here is almost all NJO jazz NOT Coliseum rock!)