Tesco and the other big supermarkets - Asda, Sainsbury's and Morrisons - are scrapping over a dwindling portion of the pie as some consumers drift upmarket towards Waitrose while others increasingly favour discounters Aldi and Lidl.
Tesco is in the midst of a £1 billion plan to turn around its fortunes but like-for-like UK sales dipped 1% in the first quarter to the end of May amid the ongoing fall-out from the horsemeat scandal.
Meanwhile, Sainsbury's is on course to gain more ground on its rival by delivering its 35th consecutive quarter of sales growth when it publishes second-quarter figures on Wednesday.
Analysts on average expect Sainsbury's to grow like-for-like sales by 1.8% during the 16 weeks to the end of September, ahead of the 0.8% growth seen in the prior quarter.
Fashion retailer Ted Baker, which started from a store in Glasgow in 1987, is set to confirm more progress abroad as it expands the British designer brand from Adelaide to Abu Dhabi.
The group is expected to post six months of higher sales driven by store openings when it publishes results for the 28 weeks to August 10 on Thursday.
Its revenues were 32.7% ahead between late January and mid-June.