James Lawton: Thorn repels tide of doubt sweeping All Black country

It's still another filthy morning of All Black foreboding, the rain clouds scudding in over the running track stadium out in the suburbs. They are accompanied by the overwhelming sense that if Bradley Carnegie Thorn, aged 36, didn't exist he'd have to be created.

The New Zealand second rower is a one-man task force against the fact that every four years the greatest rugby nation on earth becomes a nervous breakdown waiting to happen.

He strides in from training and immediately dissipates the idea that Sunday's semi-final of the World Cup against Australia needs to be seen as something akin to the outbreak of a Third World War. At 6ft 5in, and 18 stone, he remains a monolith of calm even after sitting down.

"I was raised with the Springboks as the major opposition," he says. "The rivalry with Australia is fun and cheeky and both countries like to lay wood on each other, so all I would say now is that I'm looking forward to seeing how it turns out."

He might be talking about an arm wrestle in a local bar but if this sounds ingenuous against the growing Kiwi fear that the great flanker and captain Richie McCaw is losing his battle against joining his fellow icon Daniel Carter on the sidelines, and the Australians who scavenged so effectively against reigning world champions South Africa last weekend have the means to make a nightmare of the life of third-choice fly-half Aaron Cruden, Thorn says he is a bit too far down the road to change his thinking – and still less his idea of properly expressed emotion.

He is not, after all, his young and hugely popular team-mate Sonny Bill Williams, whose challenge for a place somewhere along the three-quarter line at the sharp end of the World Cup has come with a massive concentration of publicity.

Thorn, who will go against Australia – for whom he once played rugby league – for the last time at Eden Park, has never had much use for gallery playing, as we were reminded last week when he walked away from his rare touchdown near the end of the anxiety-ridden quarter-final with Argentina as though he had performed a routine tackle. "One of my pet hates is organised try celebration, especially when the guys wait for the cameras to get on them," he declares.

Sonny Bill, who is in the room, manages not to wince.

However, if Thorn is an island, or archipelago if you like, of resistance to the idea that either the New Zealand squad or the nation has any reason to panic, there is no doubt he has given himself a heavy workload. It is underlined by the stirrings of unease which come when first Jerome Kaino, then Victor Vito seem to place in doubt the official line that McCaw's nursing of an injured foot will continue to cause no more disruption than his absence from the more strenuous training.

The flanker Kaino – who was somewhat battered in the Argentina game – said: "It's not too bad with Richie not taking too much part in training. We know our game, what we have to do, and we have guys like Victor and Thomo [Adam Thompson] who could step right in."

With all respect to the handsome Vito, whose aggressive instincts are not notably modified by the fact that he also spends some time as a male model, it is not exactly like for like. McCaw is world rugby's reigning player of the year. As much as a superb tactician, he is also a moral force. With Carter gone, and McCaw at the very best at reduced ferocity, a huge challenge has come to the leadership of scrum-half Piri Weepu.

So far he has responded superbly, from yanking out of the bar his allegedly profoundly drunk team-mates Cory Jane and Israel Dagg to some metronome place kicking to help the All Blacks step out of the ambush set by an Argentina who briefly held the lead. But taking such responsibility is a relatively late vocation and one of many New Zealand worries is that it might not quite hold – at least to the extent that would be required if McCaw joins Carter on the list of fallen.

Vito seemed to be talking up his chances of walking into the McCaw vacuum, saying: "I feel in the last few days I've put my hand up. It's a huge challenge facing everyone and it's a good feeling to believe, if necessary, you could play your part."

It will take more, though, to reassure New Zealand that the threat presented by Quade Cooper and the superb marauding of loose forward David Pocock, is not mounting with each new day.

For Thorn, the Australians will always be a threat of an especially high order. He wore their shirt in that other code, he came to understand the depth of their need to win.

"We share a lot of the same thinking and instincts out on the field and so it means that if I'm not going to get sentimental about playing them for one last time, it doesn't mean that it's not one of the most important games I will ever play."

The room seems empty when he leaves. There is more talk of the leadership that New Zealand require and who will step into the hole left by Carter and the other that McCaw might also create. A little too much of it. One thing is certain. It is a mistake Brad Thorn won't make, not as he seeks to extend his career by one more match – one that might bring a little peace to an agitated nation.