IT’S the oldest joke in the book about Scottish football, and now it could be about to take an almost surreal twist.

Usually the joke goes: “What do you call a Scotsman in the knock- out stages of the World Cup finals? The referee” – but next year it could be “The honourable gentleman” or “The MP”.

Douglas Ross, the Tory MP for Moray who caused controversy last week when he missed the House of Commons debate on Universal Credit so he could be assistant referee in a Champions League match in Barcelona, has let it be known he will quit his well-paid second job after he participates in the 2018 World Cup in Russia, if selected.

With the World Cup finals beginning on June 14 next year, Ross will have to miss up to five weeks of parliamentary duty if he goes to the World Cup as part of a refereeing team led by Willie Collum, who has been pre-selected for the shortlist of referees for next year’s tournament in Russia.

That’s a big “if”, it must be said, because Ross will only go to Russia if Collum makes it to the final list, and while Collum is recognised as one of the top 20 referees in Europe, only nine Uefa referees made it to the finals in Brazil in 2014.

Collum, a teacher, was pre-selected along with solicitor Craig Thomson as one of 20 referees from Uefa’s countries who could be chosen for the World Cup next year. England at present has no refereeing representatives despite being the country that has produced the most World Cup final referees, with four.

Previous Scots to feature in World Cup finals were George Mitchell and Bob Davidson, as linesmen in 1950 and 1962 respectively, and Hugh Dallas, who was the fourth official in the 2002 final in Japan.

Ross, who was on duty with referee Kevin Clancy as Celtic beat Hibs 4-2 in the Scottish League Cup semi-final at Hampden Park on Saturday, caused controversy before while he was an MSP, by missing a committee meeting at Holyrood.

The World Cup finals next year will be the first to feature so-called video assistant referees, allowing instant replays of major decisions such as goals and penalties, and it could be that Scottish officials might be involved in that capacity.

Tory sources told reporters over the weekend that Ross would retire from refereeing after the World Cup in any case, but would not go before then in case he deprives Collum and fellow assistant referee Frank Connor of the chance to go to Russia.

The sources said: “Douglas will retire after the World Cup but it is not fair on the other referees for him to deprive them of their potential places by going before then.”

A Tory insider told a tabloid newspaper: “Douglas was an outstanding councillor and a tremendous MSP so when the SNP hammered him on his refereeing before the General Election, the people of Moray elected him over Angus Robertson anyway.

“Plenty of his voters are proud to see a local boy doing well on the world stage and the country should be proud to back Scots – whatever their strip – if they make it to the World Cup.”