On one hand, a new broom approach is welcomed by the investment community, after the disappointing performance under Tesco lifer Philip Clarke. On the other, Lewis in particular is not very well-known to the market or analysts.
"Tesco has been going wrong for six years or more in our view, and the new CEO will need to make big and tough decisions quickly," David Mccarthy, head of European consumer retail research at HSBC, warned.
The retailer needs to refocus on being just that - a grocer – rather than the myriad other ventures – such as coffee shops, banking, TV service Blinkbox and others - which have distracted from the core business, HSBC argued.
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One of the problems appears to be that Tesco has been trapped in the tactic from its glory era: huge out-of-town supermarkets. This seems out of date when there are more, smaller offerings around the corner from consumers, and when it is much easier to shop online for those hard-to-find items.
"Consumers need to know what Tesco stands for; they need a positive reason to choose the Tesco store over its local competitors," Bruno Monteyne, senior analyst at Bernstein (and a former Tesco employee), argued in a research note.
- By CNBC's Catherine Boyle