THE Co-operative Group out-performed its rivals in the grocery market growing its sales by 16.3% over the Christmas trading period.The Manchester-based group - which bought Somerfield last year to take fifth place in the sector - now commands 5.7% of the market. It has nearly 3,000 shops nationwide.Its strong performance was driven by a £200m package of price cuts and promotions over the festive period, analysts said.Figures from research group Kantar Worldpanel for the 12 weeks to February 21 reveal that Tesco is the undoubt......for the full story register now for free or login below...