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The All Blacks' most successful coach is certain New Zealand will win the Rugby World Cup but says there are problems that still need to be ironed out.

"I think at the moment with our football, and I mean both rugby and league, there's too much bad passing and handling and putting the ball behind the man instead of them running on to it and generating speed through to your three-quarters," said Fred Allen. "Fortunately it's something that can be fixed quite easily."

Allen, whose dictatorial style and penchant for "sticking it in" to players earning him the moniker "The Needle", has a few suggestions he might get to pass on to the All Blacks, should they make the semifinals, when he goes to France next month.

Allen and his good friend former All Black Bob Scott have been invited to attend the 90th anniversary commemorations of the Battle of Passchendaele in Belgium next month as guests of honour of the Returned Services Association.

It took a bit of coaxing for the 87-year-old - "25 hours in a plane is a long time when you're old" - but Allen said he was "honoured and somewhat humbled" by the invitation.

Allen, who served as a platoon commander with the 27 Battalion in World War II before he was wounded in Italy in 1945, paid homage to the tens of thousands of men killed at the small Belgian village.

"There's a headstone in Passchen-daele above the graves of 100,000 unidentified men which says 'Known Only to God'," he said.

The First Battle of Passchendaele, on October 12, 1917, was meant to create a corridor and ease pressure on French forces, but instead 2735 New Zealanders were among the 13,000 casualties as heavy rain and mud, which was deep enough to drown in, prevented accurate artillery fire and the bringing up of reinforcements.

"We thought we had it bad in WW2 but it was nothing to what those poor guys had to put up with - it really was horrific and there were thousands of men lost in three pushes."

Allen, who will dine with the All Blacks and attend both semifinals in Paris before returning home, believes the All Blacks will be more fortunate in France than the Anzacs were 90 years ago.

"I think we will win the World Cup, in fact I think we could send another team to France who would probably end up in the final. I would say this side is the most well-drilled, dangerous and skilful side I've seen and the most likely to bring the cup back out of all the campaigns we have had."

He rated Daniel Carter and Richie McCaw as two of the greatest players he had ever seen and essential to the team's success.

But his former protege and good friend Colin Meads still remains "the best footballer I've seen in all my life".

"He had a heart as big as a lion's and he could do anything. He did the donkey work in the tight and looked after the young fellas.

"He was a rough sort of diamond and we didn't see eye-to-eye at first but his allround play was brilliant."