The board of Britain’s largest private hospital operator has backed a buyout proposal worth £1bn from its second biggest shareholder, a hedge fund manager known as “the Rottweiler”, sending its shares soaring by nearly 50%.

Spire Healthcare, which owns the Claremont hospital in Sheffield and St Anthony’s hospital in south London, said it had received a non-binding proposal worth 250p a share from funds advised by the activist investor Toscafund Asset Management.

Toscafund was founded in 2000 by Martin Hughes, a longtime City figure who has been at the forefront of many takeover situations, earning him the nickname “the Rottweiler” for his aggressive approach.

Spire said: “The possible cash offer is at a value that the board would be minded to recommend unanimously to Spire Healthcare shareholders” if a firm offer was tabled.

Its share price, which had hit a five-year low of 142p in March, jumped by 47p to 221p on Thursday, giving the company a market capitalisation of £892m.

The Toscafund approach came after talks between Spire and the private equity companies Bridgepoint and Triton fell through when Triton pulled out in March. The hospital group announced a strategic review last September and said then it was in discussions with several parties to explore a potential sale of the business.

Spire operates 38 private hospitals and more than 60 clinics across England, Wales and Scotland that delivered care to 1.36 million patients in 2025. It was founded in 2007 through the acquisition and rebranding of 25 Bupa hospitals, and floated on the stock market in 2014. Spire acquired a string of other sites and also built two new hospitals, in Manchester and Nottingham.

Just under a third of Spire’s revenues is derived from work it carries out on behalf of the NHS, such as hip and knee operations. It said on Thursday that more than 85% of NHS commissioning had been agreed for the health service’s new financial year, indicating “strong growth” for Spire in the first quarter.

The company stuck to its full-year outlook, saying revenues from private patients had continued to grow strongly, particularly from people who paid for treatment out of their own pockets.

Toscafund, which took the telecoms company TalkTalk private in a £1.1bn deal in 2021, has to announce a firm intention to make an offer for Spire by 11 June or walk away under UK takeover rules.

In 2021, a £1bn takeover offer from Australia’s Ramsay Healthcare, also pegged at 250p a share, was accepted by the Spire board but rejected by shareholders.

Peel Hunt, an analyst at the equity research firm Miles Dixon, said: “Assuming that a 250p offer is forthcoming from the second largest holder, we would not be surprised to see this deal go through.”

Spire’s largest shareholder is Mediclinic, a global private healthcare group, which holds just under 30% of the company.

Dixon said the Spire board remained “highly confident” in its standalone strategy, “as indeed we do in the opportunity for this private healthcare group on the UK landscape, irrespective of which political theme holds sway”.

Spire said it had made “significant progress in strengthening care quality, diversifying revenue streams and driving efficiencies” in recent years.

There are mounting concerns among the public and NHS staff about creeping privatisation of the health service, leading to a two-tiered system. Wes Streeting, the health secretary, has defended the growing use of the private sector.

The NHS landlord Assura was bought by the rival UK healthcare investor Primary Health Properties last August in an £1.8bn deal. The acquisition came after an intense takeover battle with the US private equity group KKR for Assura’s portfolio of 600 doctors’ surgeries and other medical facilities, which serve more than 6 million patients, and many of which are rented to the NHS.