The meeting was part of a second round of meetings the commission is holding with invited parties ahead of revealing its findings in early September. The ACS was accompanied at the hearing by members and colleagues from the Federation of Wholesale Distributors.
It highlighted to the commission the impact of supermarket buying power on competition; the need to find an accurate definition of the grocery market; and the requirement for a range of stores to promote customer choice.
ACS chief executive James Lowman said: "We had a positive meeting. Over the past few months the ACS has made a convincing case for action and we were glad to be able to debate this face to face."
He added: "The Competition Commission is now in no doubt that we reject any view that competition in the grocery market is solely about choice between large format supermarkets."