News of tough economic times ahead could be one of the driving forces behind a possible price war between Asda, Tesco and Sainsbury's, among others. The supermarket market is prone to have price wars frequently, particularly ahead of seasonal periods. This article here, explains the strategies used by Asda, Tesco and Sainsbury's, yet competition is getting stronger with European supermarkets Aldi and Lidl increasing their market share (measured by the concentration ratio). Apparently there is no price war going on, yet if consumer prices get lower and lower in the coming weeks, we may have to reconsider what really is happening.
This is a good case study to use and gives you an idea about oligopolistic markets at work.