In a move that has shocked the fashion industry, Mr Mouret cited "managerial differences" for his decision to quit.
The timing is curious. As the creative director of Roland Mouret Design Ltd, business was booming. The success of his new, beautifully tailored hourglass "Galaxy" dress, which Hollywood had adopted as the frock of the moment, sealed his reputation as a tour de force in haute couture.
A spokeswoman for the company said the designer had walked away after lengthy discussions but that the parting had not been acrimonious.
"We have nothing but good feeling for Roland, for his future and what he decides to do. It's a business decision, and about the way the company is moving. It happens a lot in the industry. It's not the first time and it won't be the last," she said.
But few in the industry felt that French-born Mr Mouret, 44, who has built the company into a global brand since it was founded five years ago, would have made the decision to work out a six-month notice lightly and without "immense pain".
Fashion sources said the move was a culmination of a "difference in creative vision" between the designer and the company's owner, Sharai Meyers, who provided Mr Mouret with the investment that he needed to create his own fashion house.
"There are two people who have different visions of how the company should move forward. They want the business to grow in different ways. With the best will in the world, both tried to make this work," said the source.
Harriet Quick, the fashion features editor at Vogue magazine, said the designer's sudden resignation had "taken everyone's breath away".
"It is a complete surprise. I think people were aware that there were disagreements along the way as there are in many companies. But this is a shock. It's been Roland's year. He's been a name to drop and women have clamoured for his clothes. To have his sudden departure at such a high point this autumn says a lot about what was going on behind the scenes," she said.
When Mrs Meyers joined forces with Mr Mouret, he had shown his first collection under his own name only two years previously at London Fashion Week.
As a struggling young designer with limited financial resources, Mrs Meyers' backing allowed him to stage catwalk shows that cost up to £100,000 to put on.
Over the past five years, the UK-based company has established itself as one of the leading international design houses. With sales in excess of £1m for his spring/summer 2006 collection, Mr Mouret has dressed everyone from Scarlett Johansson to Victoria Beckham.
Many put his success down to the renaissance of the "hourglass" shape. He has suggested that he seeks to dress "real women" rather than the ultra-thin figures favoured by others.
Mrs Meyers who, with her husband Andre Meyers, holds 100 per cent of the company's equity, said she was confident "Roland will go on to do amazing work" but that "it got to a stage where there was less common ground than there needed to be".
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