Convenience store owners have been urged not to rest on their laurels after a report showed Britons spent a record £27.4bn in c-stores in 2007.

The figures, published by IGD/William Reed Business Media, found the sector grew faster than the grocery market as a whole, with sales rising 5.1% in a year, compared with 4.1% for the entire industry.

The UK Convenience Outlook report also predicts the UK market could be worth as much as £37.6bn by 2013 as a result of population growth and more people living alone.

But experts have sounded caution after IGD/William Reed Business media figures earlier this month showed c-store numbers were down from 55,798 in 2000 to 50,734 in 2007. The trend for consolidation was leading to a "loss of choice for consumers", said Shane Brennan, ACS public affairs manager .

"We have an incredibly consolidated marketplace with supermarkets and there is concern convenience markets are going the same way," he said. There were, nevertheless, "real opportunities" for c-store retailers, he added. "We went through a long period of people shopping once a week in one location. Now people are topping up and c- stores can take advantage."

C-stores were also well placed to capitalise on ethical priorities, the report said. Their locations appealed to shoppers who wanted to cut carbon emissions, while independents could partner with local producers.

Convenience multiples formed the fastest-growing sector, with sales up 10.9% in 2007 and store numbers up 3.7%.

Symbol group sector sales rose 9.1% with store numbers up 4.2%, while the co-ops grew 6.2% with store numbers unchanged. Forecourt store sales rose £100m to £3.9bn.

Sales for the purely independent sector, however, fell 2% to £6.9m. This sector is also seeing the greatest decline in store numbers.'We have a problem...'

The Association of Convenience Stores is believed to be considering a challenge to the findings of the Competition Commission's groceries inquiry over what it calls "real problems" with the investigation.

"We are not rushing into anything and taking our time to consider the report in detail," said ACS public affairs manager Shane Brennan. "We are assessing our options on what we do next in terms of responding and where else we are taking our argument - for example in government." Interested parties have until the end of June to submit their responses to the final report, which was published last month after a two-year inquiry estimated to have cost the industry £200m.

The ACS believes the commission did not go far enough in "understanding the extent of buying power exerted by the big four grocers". It also questions the commission's analysis of c-store number trends based on National Statistics data concluded that the number of c-stores was rising.