M&S reported sales growth in the past year of about 8 per cent but Dewhirst, gaining market share from rivals, achieved a 30 per cent increase in business with the high- street retailer.
Analysts suggested that Dewhirst was winning market share of M&S supply from William Baird, Coats Viyella and a number of small independent companies.
Pre-tax profits at Dewhirst for the year to 14 January jumped from pounds 6.5m to pounds 9.6m on an overall 17 per cent increase in turnover to pounds 214m.
The company said it was reaping the benefit of a pounds 6m capital investment programme which had improved the quality of its products and shortened delivery times.
It said that the ability to respond to replacement orders was especially important.
Tim Dewhirst, chairman, said: 'We have been trained to be driven by what the market wants rather than by our own manufacturing capabilities.'
Men's suits and women's blouses were particularly successful lines.
Profit margins widened from 3.9 to 4.5 per cent, but most of this benefit was due to an improvement in the smaller toiletries side.
Profit margins from clothes were 4.2 per cent against 4 per cent. The company said it aimed to raise margins to 7 per cent.
Earnings per share increased to 5.1p from 3.5p. The dividend was lifted in line with earnings by 45 per cent to 1.45p.
The shares added 9p to close at 114p. In the past 12 months the shares have risen from 60p, outperforming the market average by nearly 50 per cent.