Sir Paul Marshall has sealed a £100m takeover of the Spectator magazine as the backer of GB News completes the next stage of his ambition to control a significant swathe of the UK’s conservative and rightwing media outlets.

Marshall, the hedge fund tycoon who already owns the UnHerd website, is also in the running to buy The Daily and Sunday Telegraph with the second round of bids by prospective buyers due by 27 September.

The tycoon, a backer of the often controversial GB News TV channel which launched three years ago, has acquired the politically conservative magazine through his Old Queen Street Ventures (OQS).

Marshall, who has been in exclusive talks to buy the world’s oldest weekly magazine for the past month, has promised to keep the Spectator an independent part of his rapidly expanding British media empire.

Marshall, who is to house the Spectator alongside UnHerd within subsidiary Old Queen Street Media, said he is “confident that OQS will be a fine custodian”.

“The plan is for OQS to make good previous underinvestment in one of the world’s great titles,” he said.

Freddie Sayers, the chief executive of OQS and editor of UnHerd, will become the publisher of UnHerd and The Spectator.

He said the Spectator will remain separate, with independent editorial and governance structures, including the formation of a new board likely to include Conservative politicians.

“It is a very different publication to UnHerd, with its own politics, atmosphere and interests,” he said. “We are committed to helping both publications develop independently.”

Marshall will chair the holding company but will not sit on the board or take a management position.

Sayers said that the plan is to “invest in journalism and be committed to the highest standards, with a dedication to the core principles that underpin a free press: accurate presentation of news and free expression of opinion”.

To date Ofcom, the media regulator, has carried out 23 formal investigations amid 13 breaches of broadcast rules by GB News relating to the TV channel’s lack of impartiality.

The Spectator chair, Andrew Neil, a former chair at GB News who said last year that hedge funds should not be allowed to own newspapers over conflict of interest concerns, is expected to leave now that the sale is complete.

Fraser Nelson, who joined the Spectator in 2006 and became editor in 2009, remains the editor of the title.

Plans for the title include “expanding the magazine’s reach in the Anglosphere and North America”, and boosting the reader experience by “innovating across technology, video and audio”.

The sale represents the first stage in recouping the £600m paid by RedBird IMI – the consortium backed by Sheikh Mansour bin Zayed al-Nahyan, the vice-president of the United Arab Emirates and owner of Manchester City football club, and the US investment firm RedBird Capital Partners – which took control of Telegraph Media Group in November last year from the Barclay family.

However, the deal was referred to UK regulators over press freedom and competition concerns.

RedBird IMI was forced to put the Spectator and Telegraph titles back up for sale in the spring after the British government published legislation to block foreign states or associated individuals from owning newspaper assets in the UK.

The top-end sale price for the trophy asset, more than 30 times the adjusted profits of £2.9m on £20.8m revenues in the last reported accounts from 2022, will give RedBirdIMI confidence that a blockbuster sale of the Telegraph titles can be achieved.

The Barclay brothers paid £20m for the Spectator in 2005.

“We are pleased this process was completed swiftly and smoothly, maximising value and providing certainty to the Spectator staff and their growing readership,” said Rani Raad, the chief executive of IMI. “The next phase of the sale of the Telegraph Media Group continues with strong interest from UK and international groups.”

The sale of the Daily and Sunday Telegraph is being run separately. RedBird IMI last month whittled down the shortlist of potential buyers for the next round of bidding.

Marshall, who is leading a bid as part of a consortium backed by Ken Griffin, the US billionaire founder of the Citadel hedge fund, is one of about four prospective buyers in the running.

Rival bidders so far revealed include the former chancellor Nadhim Zahawi. However, it is unclear if he has achieved formal commitments from billionaire backers he had held talks with about funding a £600m bid.

National World, the UK-listed media group, is also thought to still be in the frame. CVC, the private equity group behind the Six Nations tournament , is understood to have held talks with other bidders about potentially making a joint offer.

However, it is not clear how serious the talks have been or whether any have progressed formally.