The Competition Commission has received a series of warnings that the dataset used as a basis for many of its preliminary findings may be misleading. Among those drawing attention to the limitations are Tesco and Experian, the company which supplied the data.

The CC's conclusion that there is no evidence of a significant decline in c-store numbers drew heavily on data from Experian's Goad survey.

However, several parties have suggested that this data does not accurately reflect the true state of the convenience market, because it does not take into account village and suburban locations.

Tesco used the data to support its own case in a submission to the Commission in December 2006. However, it warned: "We recognise that there are certain limitations to this analysis. Experian Goad only surveys retail 'centres' (including town centres, shopping centres and retail parks), and so does not pick up changes in vacancy rates and fascia type for shops outside of these main centres (which is often where convenience shops are located)."

A Competition Commission spokesman confirmed that Experian had advised the CC that more comprehensive market coverage would have been provided by a second set of data from the company, ShopPoint. However, the CC felt this did not have sufficient historic data to accurately depict trends, the spokesman said.

ACS chief executive James Lowman added: "It is a great shame that, several months after we explained clearly why the Commission's analysis of store numbers in our sector was flawed, we are once again rehearsing these arguments. We have already pointed out that this database, which includes fewer than 4,000 convenience stores in town centres and retail parks, is in no way representative of convenience stores as a whole."

An ACS survey of Farnborough, Hampshire, revealed 23 convenience stores which were not included in the Experian data. ACS points out that IGD/Knowledge Store data, recognised as the definitive database by all the major research bodies in the grocery industry, shows a decline of about 9% in the total number of convenience stores between 2000 and 2007.

The CC said its findings were based on both Experian and IGD data, as well as figures from the Office of National Statistics (ONS), and that there was insufficient evidence to conclude the sector was in terminal decline.

However, ACS expressed its concern that the ONS data, which is based on a sampling approach, may not fully capture developments in the industry. "The data from the Office of National Statistics is as unreliable as the Experian-Goad database," Lowman said.

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