The Co-operative Group has achieved a lot since buying Somerfield. But it’s chief executive Peter Marks needs to toughen up to take on the big boys.

Co-operative Group chief executive Peter Marks was incredibly smug at the grocery analysts IGD Convention on Tuesday. The previous day he had revealed market-beating like-for-like food sales in its interim results, and is convinced the company’s ethical stance is proving to be a winner.

Marks has reason to be smug. He has managed to turn out good growth in its food business after the not-small task of buying Somerfield, while also carrying out yet another acquisition in another part of the business – taking over Britannia Building Society.

While the Somerfield integration is far from complete, Marks believes the store modernisation programme – of Somerfield and the old Co-op shops – will be complete by the end of 2010.

At the same time Marks has been driving down prices and its relaunched Simply Value range is up 80% year-on-year.

What Marks needs to learn, though, is that food is an incredibly competitive business. While the Co-op has done well over the years and has built up a loyal following, buying Somerfield has propelled it into the big time and if Marks wants to play with the big boys, he needs to toughen up.

Take Tuesday as an example. He – once again – had a little moan on stage about Asda chief executive Andy Bond’s claim to become the first genuinely transparent business in response to a “new era of democratic consumerism”.

Marks said the Co-op invented democratic business 200 years ago and insisted he was “the only truly democratic grocer”.

Marks may well be right in what he says but with grocery, it tends to be a case of who shouts the loudest wins the race.

Shoppers don’t plot the changes in business models of the supermarkets with careful precision. They are fickle and if they see an advert, read a newspaper story, or see something in stores that hits the mark, then they are more inclined to shop with that retailer.

This year all the grocers have stepped up promotional campaigns and Asda has taken a different stance with its transparency drive. Marks needs to realise that the knives will be out for a long time yet and make sure the Co-op’s voice and message is heard.

He has achieved a lot in a small space of time since buying Somerfield, and has a good shot at being Britain’s fifth biggest grocery player and taking on the Big Four, but needs to develop thicker skin.