SPFL chief executive Neil Doncaster today poured scorn on conspiracy theories that Rangers will be allowed back into Scottish football's top flight through the back door - even if they fail to win promotion through the play-offs.

Doncaster hit out amid speculation that summer talks over league reconstruction would give the Ibrox club a passport back to the Premiership.

But he did admit discussions are under way about a radical revamp of the League Cup, which could see teams enter a sectionalised group stage in July with a final before the turn of the year.

A three-year lockdown agreed at the time of the merger between the old SPL and SFL, which means the assent of all 42 clubs is required for changes to the format of the leagues, makes accelerating the Ibrox club all but impossible. But, as the league supremo unveiled Ladbrokes as their first title sponsor since 2013 - a deal worth £4m over two years - he did confirm talks were under way about revitalising the League Cup, most likely starting the summer of 2016.

"What do you think?" asked Doncaster, about the idea of Rangers being promoted. "I can't foresee that happening.

"We are in a lockdown period of three years so nothing realistically can happen in terms of league structure for three years. That period ends next summer. There is certainly a debate around the best structure for the league cup and the league.

"I think those debates are very healthy and we should continue to talk about what the clubs want. If they ultimately come to consensus then we will have change. If they don't, we won't."

Doncaster defended his six-year reign as SPFL chief executive and insisted he won't step down. The Englishman has been criticised by both Hearts and Hibs over the timing of the last-day championship meeting between Hearts and Rangers, faced further outrage over plans to extend the season due to a potential scheduling clash between the Scottish Cup final and the play-offs, while the SPFL have risked the wrath of Rangers by insisting they can't let season ticket holders in for free this Sunday.

An unrepentant Doncaster is already planning next season's play-off final second leg in the same weekend as the Scottish Cup final.

"Criticism is in the nature of the job," said Doncaster. "That is the reality of the job I took, the reality of the job I have today. Nothing has changed and anyone who comes into this role thinking it is going to be different is going to get a very rude awakening. I came into it with my eyes open. I don't personally feel the need to be praised the whole time and I don't take the criticism personally. As long as I do a good job for the clubs - and I believe that I and the team are - that is all that you can do."

The chief executive swatted aside any suggestion of double standards about accepting the proceeds of gambling at a time when the likes of Ian Black and Steve Simonsen have fallen foul of draconian rules against such behaviour.

"I think most sensible commentators see the difference between players who can influence the outcome of a game ... and members of the public and supporters for who a bet involving the game is part of how they enjoy the game," he said. "Responsible gambling is absolutely at the heart of what Ladbrokes are all about."