They allege that the Italian designer's company has produced a near-copy of one of their best- selling designs, and are suing for damages for infringement of copyright, and for passing off.
It is a David-and-Goliath struggle. Last year, the Antoni & Alison label, founded by Antoni Burakowski and Alison Roberts in 1988, sold less than pounds 250,000 worth of clothes to fashion stores such as Harrods and Liberty. The Armani empire has a turnover of more than pounds 340m.
Antoni & Alison's 'I feel amazing fantastic incredible brilliant fabulous great' T-shirt, from their spring-summer 1989 collection, gave the two designers their first breakthrough. The shirt was featured in fashion magazines, sold by Harrods, and worn by Neneh Cherry, the pop star, in a video.
When a similar T-shirt cropped up in last autumn's Emporio Armani collection, the two designers were astounded. Mr Burakowski, 30, a former student of Central St Martin's College of Art & Design, said: 'We saw a picture of it in Vogue, and we were stunned. They had changed it slightly, but the basics of the design were exactly as we had produced it.'
The new T-shirt, which was part of the Armani Jeans range, includes the words 'I feel outrageous amazing brilliant terrific great', and the Armani Jeans logo.
Antoni & Alison contacted Armani last September to protest at the similarity between the two T-shirts. Through its British solicitors, the Italian firm categorically rejected the allegations, but said that the company was concerned to preserve its reputation for distinctive products and, 'in view of the matters that you have drawn to our attention', did not intend to market the T-shirts. Antoni & Alison were far from satisfied.
Ms Roberts said: 'The image had already been used in all their advertising and their new season's catalogue. They did withdraw all the catalogues from London when we complained, but we received no apology. And the catalogues and the T-shirts were still on sale abroad.'
Now the two designers have decided to go public with their complaint. Their legal battle was featured yesterday on BBC TV's The Clothes Show. The case comes to the High Court in London on Thursday.
Mr Burakowski said that he was determined to make a stand against alleged copying of designs. 'This sort of problem is endemic in the fashion industry. Designers from abroad just take and use British fashion designers' ideas and think they can get away with it.'
In the fashion world, young designers regularly complain that their work is copied by bigger names. It is rare, however, for small companies to pursue their allegations this far. Mr Burakowski said that he had sought emergency legal aid for his action. 'Our resources are limited. We are a very small business compared to Armani.'
Antoni & Alison are best-known for their designer underwear, which sells to a very select market. Mr Armani is arguably the most influential name in contemporary fashion, introducing a relaxed form of tailoring which has transformed the modern wardrobe.
Giorgio Armani had no comment to make on the affair other than to reject all the allegations.