The expansion programmes of the big four supermarkets has resulted in a significant boost in turnover for one of the ­major contractors involved in converting and building new stores.

Results announced this week by Interior Services Group show revenues in its food retail division almost doubled in the year to 30 June from £119m to £218m, while profits leapt 44% to £5.2m.

But the company, which was appointed as the main contractor in the conversion of 80 former Netto stores to Asdas, also reported its margins had been squeezed by retailers looking to cut the cost of store refits and new builds.

They now stood at 2.4% in the company's food retail division having been 3.1% in 2010.

"The results show that all the major supermarket brands remain committed to their programmes in the UK," said ISG chief executive David Lawther. "Our margins are continuing to come under pressure and have reduced, but the supermarkets are still looking to expand and we hope to be part of that."

During the year, the company doubled its work for Tesco and carried out its 400th project for Asda. In June, it had an ­order book from retailers worth £140m, up from £113m in 2010. It predicted continued strong expansion.