Blackstone, one of the world’s biggest private equity firms, is in advanced talks to buy a stake in Ambassador Theatre Group (ATG), the owner of some of the most famous playhouses in London’s West End.

Sky News has learnt that Blackstone, which manages more than $1trn (£790bn) in assets, is close to snapping up a minority interest in the owner of the Duke of York’s and Lyceum theatres.

If completed, it will be a significant corporate transaction for a company which has staged productions of Harry Potter and the Cursed Child, Hamilton and The Book of Mormon.

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City sources said that Blackstone was expected to acquire the shareholding from TEG, an Australian live entertainment and ticketing company which bought into ATG during the pandemic.

One added that the deal would involve a stake of between 10% and 15% changing hands.

ATG has been majority-owned by Providence Equity Partners since 2013, making it a lengthy ownership period by private equity industry standards.

Providence did consider running a sale process several years ago but was stymied by the pandemic, which forced the closure of theatres and other live entertainment venues for months during a succession of lockdowns.

ATG operates dozens of theatres in the UK, with its other prominent venues including the Harold Pinter Theatre, as well as the Empire in Liverpool and the Lyric and Hudson on Manhattan’s Broadway.

In total, it owns roughly 60 theatres, having struck a deal in 2021 to buy the Golden Gate Theatre and Orpheum Theatre in San Francisco, and the Fisher Theatre in Detroit – both of which are key cities for touring Broadway productions.

Last year, it announced that it was combining its US operations with Jujamcyn Theaters to strengthen its position in that market.

The company competes with rivals including Lord Lloyd Webber’s Really Useful Group and the billionaire Sir Leonard Blavatnik, who owns the Theatre Royal Haymarket.

The valuation of ATG in the deal with Blackstone was unclear this weekend.

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Providence acquired the company for £350m over a decade ago.

In 2022, it was reported to be seeking to refinance roughly £1.2bn of debt.

ATG has a workforce of more than 4,000 full-time equivalent employees, and its venues have played host to some of the world’s most successful plays and musicals, including The Lion King, Les Miserables and Wicked.

The company was founded in the 1990s by the husband-and-wife team Sir Howard Panter and Dame Rosemary Squire, who subsequently went on to set up a rival theatrical group.

It is now run by Ted Stimpson, a leisure industry veteran who replaced Mark Cornell last year.

A renewed sale process for ATG is said to be unlikely to take place for some time.

Accounts for International Entertainment Holdings, ATG’s parent company, show it made a record operating profit in the year to 25 March 2023 of £120.5m.

It said that advance ticket sales were exceeding pre-COVID levels.

Blackstone and Providence both declined to comment.

Around 1,500 workers at Tata Steel will hold an “all-out indefinite strike” next month, a union has announced.

The industrial action at the company’s sites in Port Talbot and Llanwern, Newport, will begin on 8 July, Unite said.

The union said the walkout would “severely impact” the company’s UK operations.

It comes in response to plans to close Tata Steel’s blast furnaces in South Wales, putting 2,800 jobs at risk.

The union said it would be the first time in more than 40 years that steel workers in the UK have gone on strike.

Members voted in favour of the move in April.

Industrial action short of a walkout, including staff working to rule and a ban on overtime, began earlier this week.

The union’s general secretary Sharon Graham said: “Tata’s workers are not just fighting for their jobs – they are fighting for the future of their communities and the future of steel in Wales.

“Our members will not stand by while this immensely wealthy conglomerate tries to throw Port Talbot and Llanwern on the scrap heap so it can boost its operations abroad.”

She added: “The strikes will go on until Tata halts its disastrous plans.

“Unite is backing Tata’s workers to the hilt in their historic battle to save the Welsh steel industry and give it the bright future it deserves.”

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Tata Steel previously said it was losing £1m a day at Port Talbot and warned the situation was unsustainable.

The company said its plans, which include the building of an electric arc furnace, would mark the beginning of a new way of “competitive and greener” steelmaking.

The proposals were officially confirmed in January, with its boss TV Narendran telling MPs the decision was “pretty much” a done deal.

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Sky News first exclusively revealed details of the plans in September 2023.

Tata Steel initially offered an enhanced redundancy package to workers affected by the proposals, but this was reduced after the industrial action short of a strike began earlier this week.

Unions, including Unite, expect Labour to hold emergency talks with the company if the party wins the upcoming general election.

Alun Davies, national officer for steel at the Community union, which says it represents the “vast majority” of affected Tata workers, said it had decided with the GMB union not to take part in any industrial action for now.

He added: “If the Labour Party wins the general election it has said that it will hold emergency talks with Tata…

“We welcome this, and now feel it is important to wait for the completion of that process before initiating any significant course of action.”

The former head of a union for sub-postmasters has denied it became “too close” to the Post Office and was “flush with money”.

George Thomson, formerly of the National Federation of SubPostmasters (NFSP), also denied lacking sympathy for those who were wrongfully convicted during the Post Office scandal, which occurred following faults in the organisation’s Horizon IT system.

It comes after the TUC claimed earlier this year that the Communication Workers Union (CWU) had been blocked from effectively organising at the Post Office, and alleged the NFSP was given funds by the Post Office.

Mr Thomson, who served as its general secretary between 2007 and 2018, gave evidence at the Post Office inquiry on Friday.

When asked by inquiry counsel Julian Blake if he became “too close” to the Post Office, he replied: “No, I wasn’t.”

Mr Thomson later added: “We worked closely with the Post Office because we both needed to have a successful franchise – that’s the reality.”

The inquiry was shown an email sent on behalf of Mr Thomson in August 2013 which outlined plans for the Post Office and NFSP to sign a 15-year contract to represent all Post Office operators.

It included annual payments starting at £500,000 in 2013/14 and reaching £2.5m from 2017 to 2028.

Mr Thomson said it had taken “a lot of badgering” of the then Post Office chief executive Paula Vennells to agree to the deal. He also claimed her team “would have preferred the NFSP withered on the vine”.

Put to him by Mr Blake that they were significant figures, Mr Thomson told the inquiry the NFSP “took on new functions” as part of the deal.

When asked if the NFSP was financially dependent on the Post Office at the time when issues with Horizon were ongoing, Mr Thomson said the federation had lost 8,500 sub-postmasters in the previous 12 or 13 years, and that the money was “replacing what used to be membership money”.

He added: “It was never ever tied to Horizon.”

The inquiry was also shown a Computer Weekly article from May 2009 which detailed the cases of several high-profile sub-postmasters, including Sir Alan Bates.

The sub-postmasters told the magazine their union had “refused to help them investigate their concerns”.

Asked by Mr Blake why the NFSP did not help them, Mr Thomson said the federation had to seek permission from the Post Office first.

He said: “We did fight their cases but we asked the Post Office, ‘What are we to do as an organisation?’

“Every case that was brought to us, we took it up with the Post Office.

“You’re trying to make out that somehow we were flush with money… That’s not correct.”

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Mr Thomson said he had investigated 20 or 30 cases at the “highest level” during his time as general secretary, and would have tried to employ a computer expert had he known more about the issues with Horizon.

He said: “I’ve been around a long time – suspensions have always taken place, prosecutions have always taken place, under the manual system as well.

“We had a franchise that was in crisis and we always tried to help people.”

Mr Thomson described Horizon as “a strong system”. He added: “It’s a well-used system, and I still support it systemically as being very robust.”

However, some former sub-postmasters reacted with anger to his testimony on Friday.

They included Christopher Head, who wrote on X: “[Mr Thomson] and his organisation failed it is main overarching duty to protect its members. They are a disgrace and have no place today to be trying to represent the interests of current Postmasters, they are a sham…

“The NFSP should be completely disbanded.”

More than 700 sub-postmasters were convicted between 1999 and 2015 after errors in the Post Office’s Horizon IT system meant money appeared to be missing from many branch accounts when, in fact, it was not.

It has been branded the biggest miscarriage of justice in British legal history.