Retailers' and wholesalers' leaders are to press the Competition Commission to get more information from suppliers in a bid to prove a waterbed effect exists.

ACS and FWD representatives met on Thursday to discuss their responses to the Emerging Thinking. While the groups were unlikely to commission further major research, they would focus on smaller projects designed to tackle the specific questions in the document, said ACS public affairs manager Shane Brennan. "We want to provide more evidence of how multiples can control and dominate local markets, whether through price-flexing, below-cost selling or vouchers," he said.

The ACS and FWD will urge the Commission to force more of the 40 suppliers contacted to provide details of prices they charge different customers. Just 15 responded to the original request, and judging from these responses the waterbed effect did not appear to exist, the Commission said.

But FWD director general John Murphy said: "It is unreasonable to think the multiples have given up their price advantage since the last inquiry in 2000.

"The Commission needs to be comparing like-for-like and looking at the right categories, as some categories will be more prone than others to buying power."