The space houses everything from priceless still-life paintings by Dutch old masters to the requisite old incense burners, ancient urns, clocks - and a not-entirely-requisite stuffed monkey. But for the next three months, nestling without fanfare at the museum's unassuming heart is quite the most inspiring fashion exhibition that has been seen in this country for years.
This is, at least in part, because it has been curated with an unusual degree of intimacy and even love. Ossie Clark: A Retrospective is the result of a pairing between Cherry Gray, curator of the museum (Gray was married in an Ossie Clark dress back in the Seventies) and Celia Birtwell (Clark's creative collaborator and the mother of his two sons, Albert and George).
Clark spent his formative years in Warrington. Members of his family still live there and have offered up their own tributes to the designer in the form of clothes he designed and gave them, snapshots and tender written memories of his time at home there.
"The interior of my Uncle Ossie's bedroom is still crystal clear," writes Clark's niece, Margaret Clementson. "Concrete walls clothed in a patchwork of magazine cuttings and photographs: Elvis, James Dean, Brigitte Bardot."
Warrington is justifiably proud of a man who will go down in history as one of its most high-profile residents - along with George Formby and Lewis Carroll, both Warrington locals who have been honoured with their own retrospectives at the gallery. The designer is something of a local hero, by all accounts. "Everyone's heard of Ossie in Warrington," Gray says. "He's one of our most famous exports."
It would all veer perilously close to the sentimental were it not for two things. The first is the fact that Ossie Clark was brutally murdered by his lover, Diego Cogolato, on 6 August 1996. Second, too much attention has been directed towards his demise: his self-destructive nature and reliance on casual homosexual encounters and drugs, at the expense of his meteoric rise and exceptional talent which has, to all but the initiated few, gone unnoticed.
In the autumn of last year the relentlessly miserable Ossie Clark Diaries were published posthumously - Clark's journals for the glory years of 1976, 1977 and 1978 are missing and, save for a few happy, retrospective pages dating from 1974 which he wrote hoping they might be published during his lifetime, the lengthy tome deals mainly with bitterness and regrets.
Next came a two-part South Bank Show documentary which was equally tawdry and ultimately depressing. Certainly, neither had much to do with his creative output which remains his great legacy.
"Oh, everybody loves a good tragedy, don't they?" says Birtwell as she rushes from mannequin to mannequin, pinning descriptions against each item on display, just days before the exhibition is set to open its doors. "I got involved with this project because I wanted it to be done properly." To this end, she has worked with milliner Brian Harris and with Clark's formidable erstwhile sample machinist, Kathleen Coleman, to ensure that the clothes look just so. "I also wanted to set the record straight."
Ossie Clark dressed the Sixties: the snake-hipped, long-limbed likes of Mick and Bianca Jagger, Marianne Faithfull, Patti Boyd, Eric Clapton, Britt Ekland ... The list is endless. All take pride of place in the exhibition, their images, some of the most enduring of that period, are displayed alongside those of models including Twiggy, Marie Helvin, Carina Frost, Amanda Lear, Kari-Ann Jagger and Penelope Tree. Then, of course, there's the David Hockney connection: the famous painting by that artist, Mr and Mrs Clark and [their cat] Percy documented the fact that fashion's most glamorous couple were inseparable from the artist for a time. Indeed, he was a witness at their wedding.
Today, Birtwell - all dizzy blonde curls and clear, wide eyes - finds herself standing in front of that very painting, which has been borrowed from the Tate for the duration of the new exhibition and takes centre stage. In front of it, the actual skinny black dress trimmed in scarlet Birtwell posed in is on display.
"I can't believe I ever got into that," she says. "It was made for me and it's so tiny. I feel a little strange seeing this painting like this. It's been such a long time. And, you know, when I see it at the Tate, it's not like I can stand in front of it for hours looking at it."
Birtwell was Clark's partner at the time he produced his most brilliant work - roughly from the mid-Sixties to the mid-Seventies. All the printed fabric he used was designed by his wife, whose floating daisy, strawberry and Seurat-inspired motifs sum up the sweet unbridled optimism of that period so perfectly. Few textile designers have demonstrated such a lightness of touch since that time.
In an upstairs gallery, her sketches are displayed alongside those by her then husband, put into context by a scrapbook of pictures shot by everyone from Ossie's parents to Patrick Lichfield and David Bailey. There's Ossie as a choirboy, Ossie as a teenager in Warrington, his first fashion sketches pinned up on his bedroom wall. Later, Ossie with his classmates at the Royal College of Art and following his marriage to Celia, their skinny arms intertwined.
In the late Seventies, Clark's involvement with drugs coincided with the break up of his marriage and an acrimonious split with his wife and sons. Even today, Birtwell finds his image from that period harrowing. "It's painful to look at, isn't it?" she says, turning away.
She has no such problems, however, lingering over the clothes which come, for the most part, from her own wardrobe and from Clark's flat, retrieved not long after his death. There are the deceptively simple high-waisted, ivory raw-silk dresses favoured by Bianca Jagger. "Just look at those sleeves," says Birtwell, pointing out a bell-shaped version gathered at the wrist with an unforgiving band of elastic. "They were a nightmare to wear. And look at this little black velvet coat-dress. Oh, isn't it demure?"
Clark is perhaps best remembered for his work with chiffon, famously the most difficult of fabrics to manipulate, which, in his deft hands, becomes fluid like liquid. Jewel-coloured dresses scattered with flowers - a frill here, a tuck there - are simply sublime.
Anyone labouring under the illusion that John Galliano re-invented the bias-cut dresses of the Thirties and made them fashionable once more need only visit this exhibition to discover that Clark did so long before. Likewise, Tom Ford owed more than a little inspiration for his seminal spring/summer 1999 psychedelic collection for Gucci to the great Ossie Clark. The only shame is that no museum or gallery in London has had the foresight to put together a tribute to the designer, one which would be more widely accessible and have impact on an international stage.
As our meeting draws to a close, Birtwell points out a glass cabinet on display to one side. It contains two men's shirts, cut by Clark and emblazoned with Birtwell's prints. Lying just in front of these is a tiny gold leather jacket, intricately moulded in panels and boasting a bright purple lining. "Ossie made that for George," says Birtwell, smiling. "I think he was about eight at the time." To this day, few people cut leather with such dexterity.
Ossie Clark was, in many ways, the archetypal flawed genius. Through his inability to adjust to the unbridled talent, fame and fortune life handed to him, he died in abject poverty, having alienated many of those close to him, and consumed by resentment and mistrust. The sensational aspects of his life and death have been well-documented, dominating the public's perception of the designer since that time. Ossie Clark - A Retrospective does, indeed, if only on a small and personal scale, set the record straight just as his former wife hoped it would.
"I also hope," she says, "that when they see this, my boys will be proud of their father."
They will indeed.
Ossie Clark, Fashion Designer 1942-1996 - A Retrospective is on at the Warrington Museum & Art Gallery, Bold Street, Warrington WA1 1JG, 01925 442392. Until 29 January 2000