Tesco sits at the top of the food chain but rivals are growing peckish

Tesco’s strenth has drawn the beady eye of the CMA, which is investigating the effect of its loyalty card discounts. Photograph: Yui Mok/PA

As the UK’s biggest supermarket, accounting for more than a quarter of our national food shop, Tesco will shine a spotlight on a rapidly changing grocery market with its annual financial results on Wednesday.

With sales expected to rise almost 5% to just under £69bn, Tesco is back in the ascendant, gaining market share as household bills remained under pressure and shoppers looked for bargains.