The Scottish Professional Football League insists it has no legal power to reopen its probe into the Rangers tax case but the organisation backed calls for an independent review into how the affair was handled.

The SPFL sought advice from QC Gerry Moynihan and concluded it could not issue fresh sanctions on top of the £250,000 fine imposed in 2013 by an independent commission led by Lord Nimmo Smith.

The commission's verdict that Rangers gained no "unfair competitive advantage" for failing to disclose documents relating to Employee Benefit Trust (EBT) payments has come under serious scrutiny since the Supreme Court ruled Rangers should have paid tax on almost £50million of payments to players and other staff in the first decade of the century.

Celtic had called for a review and groups representing Aberdeen, Dundee United and Hoops fans demanded Rangers be stripped of titles.

But the SPFL's legal position is that the tax issue was irrelevant to the inquiry into non-disclosure of documents.

Moynihan's advice was that there was no power in law to reopen the case given the "principle of finality in litigation" and the fact that Rangers had paid the fine.

There were no provisions in the league rules over failure to pay tax during the EBT years nor rules regarding clubs damaging the reputation of the game.

And, although transfer embargoes were introduced in 2012 for clubs which fail to pay tax, the liability for the EBT payments lies with oldco Rangers, which went into liquidation that same year, and Moynihan advised the current Ibrox company could not be punished.

SPFL chief executive Neil Doncaster said: "What we've done is take advice from one of the finest legal minds in the country.

"Ultimately Lord Nimmo Smith's verdict was clear. His commission imposed a fine, that fine has been paid by the club. But the clear legal opinion of Gerry Moynihan QC is that we simply cannot go back and re-try this case. Any such action would be open to legal challenge and would almost certainly fail such a challenge."

Rangers also kept the "side-letters" hidden from the tax authorities as well as the Scottish Premier League and Lord Nimmo Smith wrote that the non-disclosure was "at least partly motivated by a wish not to risk prejudicing the tax advantages of the EBT scheme".

But Doncaster said: "There is a widespread misunderstanding of what Lord Nimmo Smith's commission's decision was. He found that Rangers were in breach of the SPL's rules about registering contractual documents with the league. That was not relevant to the question of whether tax was paid or not.

"We took advice at that time about what charges could be brought. We brought those charges against Rangers, ultimately Rangers were found guilty of breaches of SPL rules, and fined.

"People will have their own opinions about whether that's the right or wrong answer but ultimately that was the answer that the independent commission reached at that time.

"There were rules in place in terms of bringing the game into disrepute and people have argued that non-payment of such a substantial amount of money in tax arguably brought the game into disrepute. But that is ultimately not a matter for the league, that's an issue for the association."

The Scottish Football Association announced hours after the Supreme Court ruling this month that its unspecified legal opinion, which was not shared with the SPFL, was that there was very limited chance of succeeding with disciplinary action and limited scope for sanctions.

That position could yet be challenged by a crowd-funded judicial review, preparations for which appear to already be under way.

Meanwhile, the SFA has been approached over SPFL plans for an independent review but is yet to respond.

The league stated a review should concern the way Scottish football authorities dealt with non-payment of tax by clubs, how they applied their rules, and whether changes to such regulations have been sufficient.

Doncaster added: "This will inevitably allow lessons to be learned and recommendations to be made, to ensure effective governance so that such events can't ever happen again.

"This may enable closure to occur and perhaps go some way to re-establishing trust in the governing bodies in Scotland.

"The whole area of rules in this area across Europe has changed massively and in the first decade of the millennium there was very little if anything in terms of financial fair play rules in place across European football.

"There may be further improvements that can be made and we hope any independent review may be able to identify such improvements."