Britain brims with black and grey

The long-torso dress, the duvet coat and its friend the plush-lined raincoat, masses of tartan: These are the signatures of autumn 1980 in London. Half the stores believe in gray flannel, half in black velvet, and the delicious browns that Italian designers have promoted for fall are almost nowhere here.

You'll only find them in the camel coat, having a keen revival, and in some cocoa flannel suits imported for Harrods, for the first time, from Evan Piccone of America.

Purple is nearly gone, but not quite. It comes soft amethyst tones for tweeds, mixed intriguingly with copper and red. Ruby is the only truly bright color on the autumn spectrum here, with petrol blue a runner-up.

Winter navy is the big surprise. It is strong in wool crepe shifts trimmed in claret at John Bates, and perennial at Jean Muir, whose newest version includes moire jackets, melon-sleeved, over silk pants. Navy duffel coats will scoop up the young customers.

Evening clothes are as glamorous as ever, perhaps more so with the new 1980 mood of lushness in ruffled lace, gold-streaked mousseline, lavish flinging about of sequins. Jean Muir, a Classicist, now shows olive green angora dresses embroidered with red diamante in paisley shapes. The lush fabrics look intriguing in jumpsuits.

The taffeta ball gown, an anachronism no former swinging Londoner would be caught in, lives again and is selling enormously well from such designers as Salvador and Murray Arbeid. Pleats have gained new impetus from the designers' interest in the big Fortuny show in Lyons, due in Brighton in October. They're all busy trying to emulate the sensational pleating the Spanish designer did in the 1930s.

The wave of new formality means lots of velvet by day, usually paired in jewel tones to a soft skirt in a tartan no Scot would recognize. Genuine tartans pour forth from the traditional mills and firms such as Scotch House and aquascutum, but the current department store crop isn't like that. There's a wave of boucle, such as Stephen Marks's chunky double-breasted jackets with plain skirts, and flat worsteds (a mix of wool and acrylic) which charms with knife-pleated skirts of light blue, petrol, and cream tartan from Reldan.

Tourists are still snapping up kilts and Shetlands, since the British look is hot news. But British stores are hunting out classic looks with a different handwriting. Harrods, already selling its American tailored suits (mixes of tweed, tartan, and flannel), is awaiting shipment of other classic suits from Germany, a country whose fine tailoring poses a real threat to this country.

British fashions are back into ethnics, but these are mostly confined to Northern Europe. Reindeer and snowflakes scamper across some sweaters, Argyle patterns across others, and there are those tartan kilts. The only other geographical area that's making waves is Austria, with the grandeur of Hapsburg frog-fastened velvet and lacy blouses on the one hand, the green-and-red printed peasant dirndls and weskits on the other.

The duvet coat has been a long time coming. America embraced it last winter, and many British women longed to have it. Now it comes from many British factories, but also in enormous numbers from India. Many of these are threequarters length, and the handsomest, usually in cream calico or in gray glazed chintz, are lined with pale pink, bright blue, jade green. One British suitmaker does the navy cotton jacket that completely reverses to tweed to match its skirt -- a popular idea in these investment dressing days.

While all signs are that the duvet and the Borg-lined raincoat will be the walkaway successes of the year, real honest-to-goodness wool coats now look fresher, too.