An investor in the planned takeover of Newcastle United that received high-level support from Boris Johnson last year is a major Conservative party donor who has personally funded the prime minister’s constituency office and leadership campaign.

Jamie Reuben, 34, his father, David, and uncle Simon, who own the Reuben Brothers property development empire, were co-investors with the Saudi Arabian Public Investment Fund (PIF), and the financier Amanda Staveley, in the £300m bid to buy the Premier League club from Mike Ashley.

The deal stalled last May as the Premier League reportedly pressed PIF, whose chairman is the Saudi crown prince Mohammed bin Salman, for clarity about its structure, and whether it is a government entity.

According to leaked messages reported by the Daily Mail this month, Prince Mohammed privately contacted Johnson in June, complaining about the delay and warning him that if the Premier League blocked the takeover, it would have “a negative impact on both our countries [sic] economic and commercial relations”.

The Saudi-Reuben Brothers-Staveley consortium ultimately withdrew from the deal on 30 July, blaming the “unforeseeably prolonged process”.

In September, according to the leaked messages, Johnson asked his adviser Edward Lister to investigate the chances of the deal being revived. When Lister told the prime minister that he was hopeful it was back on, Johnson reportedly replied: “Brilliant.”

Jamie Reuben

Jamie Reuben has previously donated £700,000 to the Conservative party and Johnson’s support for a deal that was being pursued by such a substantial donor, and which followed personal messages from Prince Mohammed, raises further questions surrounding allegations of cronyism, and whether business figures and political donors enjoy privileged access to the prime minister and his government.

Under the league’s “owners and directors test” there were potentially deal-breaking concerns about a Saudi state entity owning a club, following the finding that persistent piracy of international football TV rights had been carried out from Saudi Arabia.

A Saudi takeover of a Premier League club was also hugely sensitive following the murder of the journalist Jamal Khashoggi in October 2018, in which Prince Mohammed has been implicated by the UN and other official reports.

A source with knowledge of the deal said they have been shocked to discover Prince Mohammed’s intervention with Johnson, because he was supposed to be keeping out of the deal, given the case the PIF was making that it was separate from the Saudi government.

A spokesman for Reuben Brothers told the Guardian Jamie Reuben did not contact the prime minister about the Newcastle takeover.

“We’re not denying that Jamie has a relationship with Boris Johnson and they talk,” the spokesman said, “but Jamie is quite specific that he hasn’t contacted or talked to him or Lord Lister about the Newcastle deal.”

Downing Street did not directly answer questions about whether the prime minister had contact or discussions with Jamie Reuben about the Newcastle deal, but denied seeking to influence it. A government spokesperson said: “This was a commercial matter for the parties concerned and the government has not been involved at any point in influencing the Newcastle United takeover talks.”

Jamie Reuben first donated £35,000 to the Tory party in 2012, and has donated more than £700,000 to the party altogether, including £50,000 to Johnson personally in the run-up to the 2019 Conservative leadership election. In October and November 2019, before the general election at which Johnson was elected prime minister, Reuben made two donations of £200,000, and one of £48,000.

A further donation from Reuben made in December 2019, of £123,750, was the provision of offices owned by the Reubens for use by the party. A company in which Jamie Reuben is a director, Investors in Private Capital Ltd (IIPC), has donated a total of £1.98m more to the Conservatives, including £25,000 to Johnson’s own office in his Uxbridge and South Ruislip constituency in March 2015.

Another of Reuben’s companies, Melbury Capital, states on its website that he served as the committee chairman for Johnson’s re-election campaign as London mayor in 2012 and 2019 [presumed to refer to Johnson’s Conservative party leadership campaign], and that Reuben is currently a treasurer of the Tory party.

Jamie’s father, David, made a registered donation to Johnson of £4,000 in 2008, consisting of prizes provided for auction. The Reuben family was also a substantial donor to Zac Goldsmith’s constituency of Richmond Park while he was an MP. In 2016, a spokesman told the Guardian that the Reuben and Goldsmith families had known each other well for many years and that Jamie and Dana, Simon Reuben’s daughter who donated £26,000, had become “good friends with Zac”.