By HUGO DUNCAN

Updated: 11:46 GMT, 1 January 2026

Three of Britain's biggest companies will welcome new bosses today in a changing of the guard at the top of UK plc.

Drugs giant GSK, drinks group Diageo and water supplier Severn Trent all start the New Year with a fresh face in the chief executive's chair.

Former Tesco boss Dave Lewis is tasked with turning around struggling Diageo as he becomes its third boss in less than three years.

His predecessor Debra Crew quit in July 2025 having only taken over following the death of long-standing chief Ivan Menezes in June 2023.

Cheers: Guinness owner Diageo is one of three big firms with a new boss starting today

Shares in Diageo, which owns brands including Guinness, Smirnoff and Johnnie Walker, fell 37 per cent last year and are down 60 per cent since their peak at the end of 2021 as reels from subdued sales and rising costs.

Analysts said Lewis faces the toughest job of the three taking the reins today - with Luke Miels succeeding Emma Walmsley at GSK and James Jesic replacing Liv Garfield at Severn Trent.

Garry White, chief investment commentator at wealth manager Charles Stanley, said: 'Diageo's Dave Lewis faces the most daunting challenge of the three. 

Luke Miels at GSK and James Jesic at Severn Trent are largely continuing with business as usual. 

For Diageo, the challenges verge on existential, making this arguably the toughest type of job a chief executive can inherit.'

Lewis - known as Drastic Dave for his ability to cut costs and turn businesses around - will be under pressure to come clean over his plans for Guinness given persistent rumours Diageo may spin-off the Irish stout maker.

Dan Coatsworth, head of markets at AJ Bell, said: 'Lewis must get the business back on track quickly, and that is likely to involve asset sales, big cost cutting, and a tighter focus on the company's leading brands.'

The shake-ups at GSK and Severn Trent sees the departure of two of the Footsie's most high-profile female chief executives in Walmsley and Garfield.

White said Miels takes over at GSK 'at a pivotal moment', adding: 'He inherits a company under pressure to revive investor confidence after years of lacklustre returns and a mixed record on research breakthroughs. 

'Expiring patents loom for blockbuster HIV treatments later this decade, threatening a sharp revenue hit, while pricing scrutiny from regulators in the US and Europe adds further strain. 

'At the same time, GSK must prove that its strategy, focused on vaccines and specialty medicines, can deliver. There are challenges, but no need for rapid, radical change.'

Coatsworth described new Severn Trent boss Jesic as 'a safe pair of hands' who has worked there fore more than 20 years.

He said: 'James Jesic needs to ensure the business spends money wisely, avoids the mistakes of its peer group with sub-standard performance, and stays in tiptop shape to please the regulator, customers, and shareholders.