When Dave Lewis was rushed in to take the reins at troubled supermarket group Tesco, he was candid about his qualifications, declaring: "I have never run a shop in my life."

Three months into the job and he's now directly in charge of 3,300 of them, after taking personal control of the group's underperforming UK stores chain. That means the former Unilever executive is either a very fast learner, a natural- born retailer or, more likely, is doing his best to cope with a dearth of talent at Britain's biggest retail group.

Monday’s announcement that Lewis is to take day-to-day control of the core domestic operation raised a few eyebrows in the City, and not just because of the new boss’s lack of retail expertise. There were complaints that Tesco chose to announce the move, which was part of a wider management shake-up, via an internal email to staff, rather than through a formal stock exchange announcement.

Temporary

Lewis is taking over from

Chris Bush

, who was managing director of the UK chain but has now left after being suspended in the wake of the £263 million accounting scandal. Although Lewis’s move is only temporary, the UK stores are by far the most important part of the group and their performance is crucial to Tesco’s recovery. It’s certainly unusual that news of such a major management reshuffle should emerge via an email to staff.

This form of communication with investors has become something of a pattern in the 12 weeks that Lewis has been in charge, however. With somewhere in the region of 500,000 staff, the emails always leak, of course, and there were mutterings that an official news release might have been more in order. As one commentator sniffed, Lewis is now running Tesco, “not Unilever’s shampoo and soap arm”.

The executives suspended in the aftermath of the overstatement of profits were dubbed the "Cheshunt Eight," so named after the Hertfordshire location of Tesco's head office. Several of them have now departed from the retailer but the shake-up sees one manager return to his duties with a ringing endorsement from Lewis. Head of sourcing Matt Simister whom Lewis described as one of Tesco's "most capable leaders" had "worked tirelessly" to help resolve the problems and his conduct was "exemplary".

But stocks of capable leaders look to be running low at the supermarket chain, which is a worry in a group of Tesco’s size, and with operations spread around the world.

That feeling of lack of control was evident last week, when near riots broke out at a number of Tesco stores as frenzied shoppers fought for Black Friday bargains. There were unruly scenes at other store chains but nothing as bad as those seen at Tesco.

Carnage

In Greater Manchester, police were called to seven Tesco stores in the early hours of Friday morning and several arrests were made. The scenes of carnage saw hundreds of shoppers refuse to leave stores despite being told all the heavily discounted stock had been sold.

One woman was hit by a falling television, another suffered a broken wrist and there were numerous scuffles among shoppers.

Such sites leading television news bulletins and going viral on social media sites may well have been the deciding factor for Lewis to step up.

Surpassing expectations

Aside from the shoppers who successfully bagged their bargains, one clear winner to emerge from the mayhem of Black Friday is

John Lewis

, the employee-owned department stores chain. Its takings last week jumped by 22 per cent to a record £179 million, surpassing even the most optimistic expectations, and beating the previous record of £164 million set in Christmas week last year.

Online sales surged by more than 40 per cent, with traffic to its website soaring by 300 per cent in the early hours of the morning. Records were also set by a number of stores, including its Oxford Street flagship.

Among the most popular products were tablets along with big screen televisions and coffee makers.

Reporting the stellar figures, John Lewis's operations director Dino Rocos said that, while the sales statistics were attention-grabbing, the bigger achievement was "delivering an operation which ran like clockwork", with the website coping well and the atmosphere in the stores remaining "both seasonal and calm".

Watch and learn, Mr Lewis. Watch and learn.

Fiona Walsh is business editor of theguardian.com