Lush @ Academy, Manchester, 25 Nov

"Shoegaze!"

Tonight's audience – the last audience Lush will ever play to – expresses its in-the-moment-joy, its abiding love and its inevitable frustration in all manner of ways. But none quite so effectively as the likely lad who summarises the band's entire modus in just one word, mid-set. Miki Berenyi stifles a laugh. "Yes! Used to be embarrassing but not any more. We've reclaimed it." Indeed.

For an act whose 20-year absence was actually not causing anyone any real pain, their unexpected return, announced just 12 months ago, has been a model of how to regroup with middling expectations and then quietly go about shattering them with more art and heart than even those of us who can still just about recall seeing them play pubs had dared hope for.

The event carries more baggage then your typical bow-out. Bassist Phil King (not immune to dark irony, having sported that 'Shoegaze' legend on a t-shirt at their triumphant brace of comeback shows at London's Roundhouse in May) is absent, having jumped ship last month for reasons unknown. Rumours rumble. All parties remain tight-lipped. So tonight Lush are joined by their friend Michael Conroy of Modern English, and first (and last) night nerves be damned: he is exceptional. Berenyi can't help herself as she thanks him for his contribution: "You may have noticed someone with us tonight who is shorter, blonder... better bass player..." Ouch.

Still, beforehand, tonight feels off. Not least because the show, postponed from May, is therefore the band's last only by default,  and the characterless concrete box that is the Academy feels unworthy of the occasion. It fills painfully slowly – even during the interval, it's still half-empty. Additionally, for a band so distinctly associated with the capital, Manchester feels a long way from home.

And yet, against the odds, Lush conjure a memorable last-gasp triumph. Lifted by a rapt and boisterous crowd, they deliver a fiery footnote to their awkward, glorious history. Berenyi is in no mood for tears. "So this is our last show..." she says, before they play a note. There is a chorus of (good-natured) boos. "Oh come on! You're at an event." And so – as the next 90 minutes make abundantly, deafeningly clear – we are.

Lush play tonight with an animal hunger only usually accessible to those just starting out. Or those, perhaps, who see the end in sight. From the front of the hall, it's overwhelming: the sound mix full and bright, and beautifully loud. The set they play is the one they've polished throughout the year. The spiralling clatter of De-Luxe to begin, the in-the-clouds elegy that is Monochrome to finish.

They curate themselves with taste: the diamonds from their gleaming catalogue (the best songcraft, on reflection, of their peer group) are, whaddya know, fan favourites too. They pick the bones from Spooky and Split, but largely pass on the spiked pop of Lovelife. In there, scattered throughout, is the Mad Love EP, still their most perfect release: Leaves Me Cold, Thoughtforms, a ferocious Downer. The latter kicks and bucks, a two-minute thumbs-down to the multi-layered arrangements and deft harmonics of much of what was to follow.

"It's like a fucking marathon!" Berenyi had gasped at the climax of their second Roundhouse show but now she launches herself into the tumultuous instrumental section of main set-closer Sweetness and Light. Kiss Chase. Etheriel. An explosive, note-perfect Nothing Natural. How these songs have grown with time. Out of Control, Berenyi's love letter to her teenage daughter and the lead track from the comeback Blindspot EP, breaks hearts across the room but Berenyi pulls the rug: "She's at Savages at Brixton Academy tonight. There's fucking loyalty for you, eh?"

We want more of course. Not just tonight, where extended ovations during the encores cause Berenyi's voice to break just a little. "Thank you so much for being in the vibe tonight," she says. "The highs really have been fucking brilliant." The lows, clearly, have not. And therein lies the clue to it all. Because, you suspect, no matter how many glories the future might have held, re-assembling something as unnatural and unwieldy as a band, is surely the hardest work. Years apart and then shoe-horned together again into tour bus hell.

"But can they do it on a wet Tuesday night at Stoke Sugarmill?" cry the grim forces of commerce and an industry far uglier then the one they exited two decades ago. Ultimately, surely, Lush just didn't need the hassle. And who can blame them? Still, we want more. And while Emma Anderson appears nothing other than relieved as she tosses her pick in the air and removes her guitar for one last time, she and Berenyi surely still have songs to sing. A faint hope, but one now shared by many.

In summary, then: a secret comeback gig that confirmed they were twice the live act we remembered; 6,000 fans over two nights in London to follow up, two sold-out American tours; a host of US, UK and European festival smash-and-grabs. Oh, and an EP of new songs that went toe-to-toe with their very best. They're entitled to hold their counsel for now, of course, and we should allow them that. But this was a beautiful story, an adventure that scorned nostalgia and saw Lush bloom anew with spirit and with grace. Mad love. None madder.