Dave King breached financial rules by failing to extend his offer to other shareholders when "acting in concert" as he seized control at Rangers.

The South Africa-based businessman became chairman at Ibrox after a boardroom battle with Mike Ashley's representatives ended in March 2015.

The City of London's takeover appeal board ruled on Monday that Mr King had breached the City Code on takeovers and mergers by "acting in concert" with the 'Three Bears' in acquiring a stake equalling more than 30% of the total shareholding in Rangers International Football Club PLC.

In its ruling, the watchdog found Mr King had coordinated the purchasing of the share block with George Letham, George Taylor and Douglas Park which should have triggered a move to extend the 20p per share offer to other shareholders.

The appeal board said the evidence of Mr King and Mr Letham acting in concert was "overwhelming" as an email chain between the pair, coupled with their involvement in two previous buyout attempts together, backed up the accusations.

As a result of its findings, Mr King will have to offer 20p per share to other shareholders.

The City regulatory body concluded: "Over the last two years Mr King has had ample opportunity to disclose documents and to provide other evidence to rebut any deeming, presumption or inference from the evidence that he was acting in concert with Messrs Letham, Taylor and Park. He has not done so."

Mr King had appealed against the initial findings of the takeover panel last year, arguing he was separate from New Oasis Asset Limited, a British Virgin Islands company which acquired his 14.5% shareholding in Rangers from institutional investors in 2015.

The appeal board found New Oasis was ultimately owned by Mr King for "the benefit of himself and members of his family" through a Guernsey-based trust.

The appeal board noted: "We have reached the conclusion, having regard to the grounds and basis of the appeal and taking account of all the evidential materials placed before the board, that Mr King was acting in concert with Messrs Letham, Taylor and Park in the acquisition of the shares in Rangers on December 31, 2014, and January, 2, 2015. On the 'acting in concert' point we uphold the findings and ruling of the committee."

The takeover appeal board also criticised the businessman for a "lack of cooperation" in its investigation.

In response to the watchdog's findings, Mr King said the complaint against him had been made by former chairman David Somers in the old board's "efforts to preserve their positions without regard to what was best for Rangers Football Club, its supporters and shareholders".

He added: "It is my belief that the takeover appeal board has not understood the true nature of what occurred at Rangers and the tremendous role that the activism of supporters played in ensuring regime change.

"I am only one of a vast number of Rangers supporters and shareholders who fought to rescue our club. The Rangers Football Club should never have become caught up in a takeover struggle. Those who placed it in that position bear a heavy responsibility."

The 61-year-old did not "follow the logic" of the City body and said if he was to offer 20p per share to all shareholders just now, it would be "rejected by the overwhelming majority".

Before taking control at Rangers, Mr King settled a £44m bill with the South African tax authorities after pleading guilty to 41 counts of contravening income tax legislation following the revenue service's pursuit of him for around £222m.

In the course of that litigation he was the subject of a restraint order in Scotland before it was lifted in November 2012 as he initially sought to buy a stake in Rangers newco.

Mr King claims to have invested around £20m in Rangers oldco, formerly The Rangers Football Club plc, in 2000.

He unsuccessfully applied to oldco administrators Duff and Phelps to be listed as a creditor during their attempts to strike a deal and avoid liquidation.

Around the time his group's move to seize control of the Ibrox boardroom, the Scottish FA ruled it was satisfied he was "fit and proper" to hold a position on the Rangers board.