The Competition Commission is under pressure to rethink its verdict that c-store numbers are not in decline, after it emerged the supplier of the data on which it based this view had warned it was not suitable for this purpose.

In the provisional findings in its groceries inquiry, published on 31 October, the commission said the data it examined had not provided sufficient evidence that numbers of small stores were falling in the face of competition from big supermarkets.

This angered c-store leaders, who claimed the inquiry team was ultimately swayed by an Experian Goad survey, which showed that when a supermarket entered a local area, numbers of c-stores actually increased slightly.

They have repeatedly pointed out - in vain - that this data set covers town centres and retail parks only and does not measure the entry and exit of small stores in villages and suburbs - key heartlands for the convenience centre.

This week, however, a source close to Experian and the commission told The Grocer the commission was warned the figures should not be used to establish the health of the convenience store sector as a whole.

"Experian responded to a request for data from the commission for a report into the UK convenience sector," said the source. "The commission was made aware from the outset that surveyed Goad data relates predominantly to high street, shopping mall and retail park locations and was not going to provide the breadth of coverage required for an in-depth analysis of the UK convenience sector.

"Experian advised the commission that far better coverage would be provided by its ShopPoint data, which combines data from both Goad surveys, list data and desktop research, and more than doubles the number of outlets covered by Goad surveys."

A spokesman for the commission insisted it had not been over-reliant on the Experian Goad data, he said.

"The conclusions we've come to haven't been as a result of one particular data set.

"We've balanced a range of evidence. We're aware, and it has been pointed out, that different data covers different things.

"The Experian data focuses on town centres and the entry and exit of small and specialist shops in these town centres - one of the fundamental issues that led to this inquiry."

The commission's apparent intransigence on this matter has not deterred the ACS and the FWD from jointly submitting fresh figures to the commission, which they say demonstrate the number of small shops in the market is falling and that the Commission has got its facts wrong.

The submission includes a report by Verdict that shows that while superstore numbers rose from 34,000 in 1996 to 35,000 in 2006, numbers of small stores fell from 35,000 to 32,000 over the same period.

The Verdict research will be backed up by figures from FWD members that will show by how much their retail customer numbers have declined since 2000, the last time there was a full groceries inquiry.

The Commission said it was prepared to listen to any new evidence.