CELTIC icon John Hartson has appealed for calm in the wake of the latest refereeing storm to hit Scottish football.

There has been an outpouring of frustration from both players and supporters of the SPFL Premiership leaders following Sunday's handball-gate incident against Inverness Caley.

Celtic have since written to the SFA seeking clarification on the decision not to award them a penalty in the William Hill Cup semi-final, which the Highlanders went on to win 3-2 after extra time.

It is also an incident which has caused many Hoops fans to blast the officials involved, including whistler Steven McLean and additional assistant referee Alan Muir, who both missed Josh Meekings' glaring handball which has seen the Caley star offered a retrospective ban, which he will contest.

However, while Hartson understands their frustrations, he is keen to keep a sense of perspective to halt a witch-hunt being launched against the whistlers.

"It's happened over the years. Hugh Dallas had a coin thrown at his head, there's been reaction to big decisions against Celtic," said the former Welsh internationalist.

"There has to be a sense of calm because I think the referee was genuinely trying to do his job and the guy has missed a big call.

"He didn't not give a penalty on purpose, he obviously didn't see the handball otherwise he'd have given it."

Hartson added: "It's always happened, hasn't it? Referees miss big decisions. It cost Ireland a World Cup spot with Thierry Henry's handball. It'll happen again."

Of course, the man who banged in over 100 goals in green and white over a five-year spell fully understands the anger and angst caused by Sunday's howler.

Not only did it deprive Celtic the opportunity to get to a major final, it also denied them the chance to build towards a domestic Treble.

Hartson joined the Parkhead giants the summer after they last achieved the feat in 2001, but is still aware of what it would have meant to have replicated the accomplishment under Ronny Deila this season.

He said: "There's a lot of anger, a Treble was at stake. It was a massive mistake, everyone in the ground could see it was a handball, it's a sending off and penalty, Celtic score and it's 2-0 and game over.

"Instead, the referee misses it, Inverness come out, they get a big call themselves, Craig Gordon's ridiculous challenge to give a penalty away and get sent off. Celtic are then up against it as they have to play with ten men.

"Everything has gone against them on the day. If I'd have been on the pitch I'd have been in the referee's ear, swearing my head off, but I wasn't. I'm quite relaxed, I watched it at home. As a player you've got to realise they react and say things."

Hartson, who was speaking at the launch of his charity foundation's testicular cancer awareness campaign, added:" I'd like to think at the weekend it was a poor decision, he obviously thought it hit his shoulder or the side of his head because if he'd seen it he'd have given the decision.

"You're angry for weeks. It's cost Celtic a famous Treble, a historic Treble which, for Ronny Deila in his first season, would have been a magnificent feat for him. It's cost the players potentially as they still had a bit of work to do in the league and still have to win against Falkirk in the final.

"Everybody is angered, Celtic feel extremely disappointed. I can understand that part of it, but it'll happen on Saturday when there's big decisions.

"It's because of the Treble talk that's why they've acted this time as they're angry and rightly so, they have a reason to be, but I don't know what purpose the letter serves."