There are fears the Competition Commission's hurry to complete its grocery investigation will be to the detriment of the inquiry.

Although the body has two years in which to conduct the inquiry, it has stated a desire to report well within that. The timetable slipped after a delay to Emerging Thinking, but at present the inquiry team intends to reveal its conclusions in November - more than five months before the statutory deadline of 8 May 2008.

In its response to Emerging Thinking, the Federation of Wholesale Distributors said it was concerned at the timetable and "a seeming rush to complete it well within the time allowed".

Meanwhile, The Co-operative Group, in its latest submission, said: "We very much hope the Commission timetable will allow for detailed and additional submissions to be made once the outputs of its further work become known, including sufficient time to enable us to carry out primary empirical research of our own.

"Without this, we are fearful that second-round hearings, which look set to provide the principal debating forum for all of the substantive issues, may deliver sub-optimal outcomes. That will, in our judgment, be unfortunate when the largest consumer market is under scrutiny."

A Commission spokesman said: "No-one has ever accused us of not being thorough. Our timetable gives us a bit of breathing space."