You could argue that refereeing interpretations played a significant part, but there was a distinct impression at the Rugby World Cup that the openside flanker had been restored to the position of being the most critical player in a team.

It is hard to imagine New Zealand would have hauled themselves over the line in the final without the brilliance of Richie McCaw. David Pocock drove Australia on with performances of ceaseless excellence, and Sam Warburton’s importance to Wales became clear when they struggled to find their shape after his controversial sending-off in the semi-final against France.

By the same token, it is hard to separate Scotland’s woes at the tournament from John Barclay’s personal battle to find form. An outstanding openside can turn a decent team into a very good one, as Barclay did most spectacularly for the Scots against Argentina in Buenos Aires three years ago. However, the 25-year-old never quite found his rhythm in New Zealand.

It was hugely frustrating for Barclay, whose performances in the 2010 RBS 6 Nations marked him out as the best No.7 in the northern hemisphere last year. He invested a huge amount of emotional energy in the World Cup, and came home from the competition feeling he had let himself down.

“I was gutted at the end of it all,” he said bluntly. “We knew what we had to do, but we didn’t put it on the pitch. I knew I hadn’t played particularly well, perhaps because I was slightly undercooked going into it. It was as much about timing as anything else. You have to be at your best in a World Cup and too many of us just weren’t.”

Like Chris Cusiter, his friend and Glasgow team-mate, Barclay gives the impression that he put too much pressure on himself in the build-up. Cusiter’s preparations amounted to a race to be fit after a long injury lay-off, while Barclay was withdrawn from Glasgow games at the end of last season to begin readying himself for the tournament.

Afforded a two-week rest after their return from the World Cup, the two players and their partners took a holiday in Portugal before clocking back on at their club. “Chris hadn’t enjoyed New Zealand, although that was for different reasons from me,” Barclay said. “He didn’t have a lot of game time, which was hard for him.

“We didn’t do much in Portugal. We just relaxed, played some golf, had dinner. There was no training as such, but I remember we went for a run one morning and talked about the importance of trying to enjoy rugby again.

“It can get you down sometimes, but you have to remind yourselves that you’re doing what you love to do. You have to make an effort to enjoy yourself and not worry about all the external pressures in the game.”

You could call it living in the moment. You could call it seizing the day. Whatever the philosophy, it seems to be working for Glasgow. Even before their World Cup players had returned, they had claimed the scalps of Leinster and Cardiff in the RaboDirect Pro12 League. With their Scotland contingent back home, they have since beaten the Ospreys and Aironi in that competition and, spectacularly, Bath in the Heineken Cup.

Cusiter has looked rejuvenated. Richie Gray seems to have acquired the Midas touch as far as match-winning tries are concerned. Barclay is still perhaps a nudge or two below his best, but he is picking up form with every game. And winning matches is always more enjoyable than the alternative.

Barclay said: “I came back to Glasgow with a focus on enjoying my rugby again. There’s still a lot of pressure around the games, but it’s not like the kind of pressure you get at a World Cup. It helps to remind you why you started playing rugby in the first place.

“It’s a good environment at the moment. You have to make the most of these times. After a good win, it’s nice to relax, have a couple of beers and forget about the pressure for a while. Of course you can’t go overboard, but I think it’s important that you should celebrate a good victory.”

The odds are still stacked against a Glasgow win in the European tournament in Dublin tomorrow. Leinster, after their 16-16 draw at Montpellier last weekend, know the importance of home victories as well as Glasgow do. The Irish side are also the reigning European champions. “When we were out in New Zealand we heard about Glasgow’s win there a couple of months ago,” Barclay said. “That was an amazing result for a young squad. I know it will be a very different Leinster team this weekend, but we can still take some belief from that win.”

Of course, Barclay also has the small matter of his own future to sort out. Suggestions that he is on the point of following Gray to Sale have been rubbished by Glasgow officials, but the situation is still in flux. However, like Cusiter, who is also out of contract at the season’s end, the more Glasgow win the more inclined he will be to stay put.

“I really don’t know what I’m going to do yet,” Barclay said. “At the start of the year I was thinking I should maybe be thinking of looking around and moving on, but at the moment it’s quite an exciting time at Glasgow.

“The changes at Murrayfield with increased budgets for the pro teams and the move to Scotstoun mean things are shaping up quite nicely. I have to sit down and think what’s best for me, but what’s happening at the moment does tip the balance more towards staying.”