AS is wholly self-evident, no primetime TV costume drama can function without costumes. Continuing a long and distinguished BBC tradition, The Cazalets last Friday made an immaculately attired small-screen debut, with the series's eponymous aristocratic family flouncing around their stately pre-war Home Counties pile in elegant upper-crust togs which apparently issued from Savile Row 60 years ago.

In fact, the Cazalet dynasty's fine clothes were expertly hand-made by one man working in a former Communist Party bookshop in a no-nonsense proletarian sidestreet in downhome Partick, Glasgow. The shop's anonymous appearance offers no clue as to the deft sartorial craft practised within.

Its owner, Steven Purvis, does not emblazon his name above the frosted-glass frontage of his premises. Indeed, Purvis's tailoring business whispers its presence to passers-by via a tiny card discreetly taped low on the door, just above the bell that the cognoscenti are required to press for admittance.

''Fashioned So Smartly'' the card says in jaunty script, above a line drawing of three dapper chappies in fifties-vintage raincoats, twirling canes. In its own way, it all amounts to a suitably understated testament to the word-of-mouth nature of Purvis's burgeoning role as a creator of timeless bespoke schmutter for discerning ladies and gents.

As well as bringing to life the work of various TV costume designers, Purvis has created a wide range of theatrical outfits for opera, ballet, and panto. Monarch Of The Glen matriarch Susan Hampshire loves the screen outfits Purvis fashioned for her - she sent him a note of thanks - while her co-star, Richard Briers, can't be parted from his gaudy tweed plusfours (the secret's in their non-scratchy lining).

Additionally, Purvis has clothed wicked witches, as well as equipping angels with light-up wings. Last year he dressed Scottish Opera's 20-strong male chorus of high priests in ''Tubi-grip'' knitted dresses with long suede aprons over them, successfully managing to iron out the many variables pertaining to the middle-aged male form.

In addition, Purvis tailors suitable suitings, dashing raincoats, and frothsome frocks which all lend drama to the everyday lives of his increasing roster of personal clients. A raffishly stellar bunch, they are too.

''It's not done to say exactly who they are,'' says Purvis. ''There are musicians, restaurateurs, TV bods, architects, advertising folk, the occasional journalistic derelict. . . all the stars of stage, screen, and Labour Exchange, basically.

''Apart from my youngest client, my two-year-old daughter, they're all professional people who want what they want - something a bit different that they can't be bothered trying to find in shops.''

A crucially different part of the Purvis experience is provided by his unique collection of cloths and fabrics. ''I hoard tweeds,'' he says. ''Over the years, fabric salesmen have got to know, and so they come to me with mill clearances, end-of-line stuff.''

Such are Purvis's connections that his Partick workshop stocks the same traditional 18oz whipcord that provides The Duke of Edinburgh with a new coach-and-four driver's suit every year. From Savile Row to Dumbarton Road, he's got the self-same boldly checked Holland and Sherry tweed, woven in Italy, in which Chris Eubank struts his stuff.

And for the ladies? Subtly kooky tweed from Linton's in Carlisle, perfect for a little Chanel-inspired suit. Price? Made-to-measure men's suits for about 500 sovs; women's from #375.

For quality and fit, your Purvis item will surpass any off-the-peg designer-name item costing half as much again. Pop along to Savile Row for a fitting and a geezer will find himself shelling out #1200-#2000.

Purvis's own training is a little less formal than Savile Row. ''As a skinny teenager, I could never buy any clothes that fitted me. It was the start of the seventies, boutiques. Everything was too big, plus I couldn't afford it.

''So I began at 16 with my mum's sewing machine, making myself trousers, nothing elaborate. I'd take stuff apart, see how it worked. My one abiding rule has always been that everything I make should never have a homemade look. I always wanted the finish to my clothes to look professional. I didn't want to go out of a night and hear the great Glaswegian put-down: 'Make that yourself, did ye?'''

Another question: how did Partick end up making an impression on The Cazalets, an English-made TV show that hopes to conquer the globe over the course of another two projected series?

''I'd happened to work with The Cazalets's BAFTA-winning costume designer Frances Tempest on an earlier, one-off drama, Bloodlines, set in Glasgow and Edinburgh. She's a stickler for detail, and I think she was impressed that I knew how to hand-close long seams, and could get fabric-covered belts and buttons.

''There are no short-cuts for TV. On screen, it shows. There was a great compliment to me when Joanna Page, who plays glamorous Zoe, walked on set for the first time in a grey coat I'd made with an astrakhan trim - the cast burst into applause.''

What fashion will next be seen on Glasgow streets from Maison du Purvis? ''Gaudy tweed flat-caps. I've never done many hats, but I recently found some flat-cap patterns at the Barras in Glasgow that came from a recently-closed East End firm, Gelfers.

''The best thing for the future is that I know I've improved in the past two years since I began working totally full-time for myself - and I know I can continue to improve. In tailoring, you learn and learn, and never stop learning.''

l You are advised to check out the happenin' threads on The Cazalets over the next five Fridays on BBC1 at 9pm

Reaping as he sews for stage, screen, and skinhead scooterboys

l Educated at Hutchesons' in Glasgow and Glasgow School of Art, Steven Purvis initially joined his father in his signwriting and poster business, Norman R McLean. ''For years, it was my dad's responsibility to create by hand the large Calmac ferry timetables that were displayed at every pier up and down the West Coast.''

l Purvis set up his first clothing workshop while he was in his final year at

art school. ''As a kid, I was always going to art school. Beyond that, I had no plan. Oddly enough, years later, after

I'd become a tailor, my brother told

me something my dad had told him, but not me: our grandfather had

been a tailor at Edinburgh Castle between the wars, making and

altering uniforms.''

l Purvis's career in clothing has encompassed design and manufacture for Scotland's leading retailers. He has been a guest lecturer at Glasgow College of Commerce and Strathclyde University.

In the late eighties he co-managed Campbell Purvis Manufacturing, which created samples for Vivienne Westwood, Marks and Spencer, Paul Smith, Nigel Cabourne, and many other notable names.

l Since setting up fully solo in Partick three years ago, Purvis's stage clients have included Scottish Opera (Aida,

Dalibor, Hansel and Gretel, Madame Butterfly); the King's Theatre, Glasgow (Mother Goose); Scottish Ballet

(Carmen), and the Royal Shakespeare Company (Richard II). Purvis-made costumes have featured on Channel 4 in A Young Persons' Guide To Becoming A Rock Star and in the BBC's Bloodlines and Monarch Of The Glen.

l Purvis's tailoring clientele ranges from skinhead scooterboys seeking shiny mohair suits for northern soul

all-nighters to advocates who have

to attend the High Court in formal tails. ''The skinheads demand the most

precision - lapels have to be 21/4 inches!'' If it can be worn, Purvis will make it, everything from wedding dresses to leather jackets.