The Indian conglomerate which owns Gleneagles resort in Perthshire has acquired a 24.5% stake in BT, sending shares in the telecoms giant soaring by more than 8.5%.

Bharti Global, which was founded by billionaire Sunil Bharti Mittal in 1976, has agreed to buy the shareholding of Altice, the French media giant, for an undisclosed amount. One report valued the deal, which would make Bharti the biggest shareholder in BT, at around $4 billion.

Bharti, which has interests in telecoms, media, space, hotels, and other sectors, hailed the deal as a “vote of confidence in the UK as an attractive global destination for investment, with a stable business and policy environment attractive for long-term investors".

It may be seen as a boost to the Labour Government and hopes to restore the prestige of London, after the City lost several major listings to other international financial centres.

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However, Bharti said it has “no intention of making an offer to acquire the company” as it endorsed “BT’s goal to transform the UK’s telecoms landscape by building fibre, rolling out 5G technology and developing market-leading services to live, work, game, and learn”.

Mr Bharti Mittal, chairman of Bharti Global, said: "This investment demonstrates the confidence we have in BT and in the UK.

“BT has a strong portfolio of market-leading brands, high-quality assets and an experienced management team with a compelling strategy mandated by the BT board to deliver value over the long term, which we fully support."

BT had previously owned a 21% stake in Bharti Global's telecoms arm, Bharti Airtel, between 1997 and 2001, and had two seats on the board of the company.

Bharti Global has through its subsidiary Bharti Televentures UK entered into a binding agreement with Altice to buy a 9.99% stake in BT. A further 14.51% will be acquired pending national security clearance from the UK Government.

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Altice, which is controlled by French-Israeli billionaire Patrick Drahi, had been upping its stake in BT in recent years, but more recently has struggled under the strain of debt. It has been selling off assets.

“The news Indian telecoms firm Bharti is taking a major stake in BT is reflective of a big power shift between the two companies," said Russ Mould, investment director at AJ Bell. “Around the turn of the millennium, it was BT which had a substantial holding in Bharti, as well as two seats on its board.

“Bharti is buying its stake from French telecoms tycoon Patrick Drahi’s vehicle, Altice, and the news will likely be greeted with some relief by shareholders as it holds the promise of a bit more stability.

“Drahi has been selling assets to pay down debt so his stake in BT represented a significant overhang on the shares.

“This situation won’t be resolved overnight given Bharti is acquiring the stake in two tranches, with the second tranche dependent on regulatory clearance. Inevitably there will be speculation about what Bharti intends to do with its stake but, for now, it is ruling out any bid for BT.

“Investors are not able to extrapolate anything about valuation either given the price Bharti is paying has not been disclosed. Management will be glad to hear Bharti are supportive of the company’s current strategy, although clearly they will want to see evidence of progress that can revive a share price which has gone nowhere in the last five years.”

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Allison Kirkby, chief executive of BT, said: "We welcome investors who recognise the long-term value of our business, and this scale of investment from Bharti Global is a great vote of confidence in the future of BT Group and our strategy.

"BT has enjoyed a long association with Bharti Enterprises, and I'm pleased that they share our ambition and vision for the future of our business.

"They have a strong track record of success in the sector, and I look forward to ongoing and positive engagement with them in the months and years to come."

Shravin Bharti Mittal, Sunil Bharti Mittal's son and managing director of Bharti Global, added: "We review global investment opportunities in the world of technology from digital infrastructure to software.

"BT is well known to us from the long association with Bharti, so we are pleased to have this opportunity to acquire a significant stake in the company.

"We believe that BT is poised for leadership in the telecom arena, especially home broadband services."

Shares in BT closed up 11p, or 8.43%, at 141.5p.