This time, chairman Sir Derek Morris is acutely aware of the pressure for a fast result. On March 19, the secretary of state for trade and industry, Patricia Hewitt, set an August 12 deadline for the commission's report on the bids for Safeway by Asda, Morrisons, Sainsbury and Tesco.
Whereas the last report into the supermarkets was a market inquiry where the length of the investigation was not a major issue, the latest inquiry is looking at mergers where timing can be crucial.
Talking to The Grocer this week, Sir Derek says: "We normally have three months for a single merger and that's tight. This gives us under five months for four mergers, and everyone accepts there are myriads of local dimensions.
"We know there is a huge amount to do in that time, but we are trying to gear up our resources and our work programme to meet that timetable.
"We expect the parties to co-operate with us as much as they can to meet that timetable."
The Commission has certainly hit the ground running this time. On the same day as the DTI announcement was made, letters were sent to the four bidders asking for their main submissions and enclosing in-depth questionnaires. Once that information is in, the Commission will publish the issues letter which will identify the main factors on which a decision will be based.
Sir Derek says meetings with the four companies have been arranged, and the first store visits are imminent.
"We will go round and look at stores as we did with the last investigation, particularly if there are new formats or new types of operation, which can happen in a changing market. So, when we are in a hearing discussing different formats, we will have a clear idea in our minds."
The hearings will begin shortly after the issues letter is published and will involve the bidders and any significantly sized bodies which wish to give evidence.
Most of the hearings will be in private to protect any commercially sensitive information that companies have to divulge. But there is likely to be a public hearing, too.
Sir Derek says: "We are increasingly moving towards having at least one public hearing [per inquiry]. One of the criteria is whether there is a particular consumer interest, so this is one we would look at pretty closely." If there is a public hearing, it will need to be early on and will probably feature senior executives outlining their cases, he says. Discussions about a public hearing are ongoing, but there are problems getting so many main parties together at relatively short notice.
Once the hearings are over, the analysis will begin. For Sir Derek, there will be a sense of déjà vû about some of the arguments as there was a lot of work on local competition during the last supermarkets inquiry. How to determine isochrones ­ the catchment area of each supermarket ­ is likely to be one of the main issues up for debate. He says: "We eat, sleep, drink isochrones. From the OFT paper, you will see there is a lot of uncertainty about the parameters of the isochrone analysis.
"That was one of the reasons everything was referred to us, so we are working flat out on that at the moment."
He refutes any suggestion that he is returning to unfinished business from the earlier investigation, insisting that everything was completed to his satisfaction before that probe was handed over to then DTI boss Stephen Byers.
Once the analysis is completed, the panel will be in a position to take a provisional view on whether any of the takeovers would be against the public interest and on possible remedies, such as store divestments. A second phase of hearings discussing the possible remedies will follow before the final report can be delivered.
Sir Derek is determined that his panel's verdict will be the final word on the issue, and has a warning for any of the parties who may consider challenging it: "We have to go through a lot of detail and analysis and come up with a defensible and a robust solution. And when I say robust I mean under judicial review."