Martin Johnson has written off Wales joining him as a World Cup winners this autumn and questioned whether they would be Grand Slam champions if the 2019 Six Nations was replayed.
The England and Lions legend became the first, and so far only player from the northern hemisphere, to lift the Webb Ellis Trophy when beating Australia in 2003 in Sydney.
Warren Gatland secured his own special place in the history books this month, guiding Wales to a third Grand Slam in his 12-year reign.
The 25-7 demolition of 2018 Grand Slam champions Ireland last weekend saw Wales take their record-breaking run to 14 successive wins.
They also usurped Joe Schmidt's side to become second in the World Rugby rankings - with only the All Blacks in front of them.
It given Wales a massive shot in the arm for their World Cup campaign this autumn and confidence abounds Gatland's team can better the run to the semi-finals back in 1987 and 2011.
But England colossus Johnson has poured cold water on Wales' hopes for Japan believing the Six Nations winners will be less effective on neutral grounds than their Principality Stadium home.
"If you replayed the Six Nations again in the next couple of months would you get the same result? Possibly not," said Johnson.
"England's performance against Ireland was probably the single most impressive performance of the tournament.
"They then had a bad second-half in Wales and blow a 31-point lead against Scotland.
"Wales were 16-0 down at half-time against France and won it on a pass that made you think 'goodness don't throw that'."
And on Wales' World Cup hopes, Johnson who coached England in the 2011 tournament before quitting after their last eight defeat to France, isn't as upbeat as some over the chances of Gatland getting his hands on the ultimate prize.
"I don't think there's any definites out of the Six Nations. England, Wales and Ireland are all pretty close to each other," added the former Leicester Tigers lock, who also captained the Lions on their 1997 and 2001 tours.
"The atmosphere in Cardiff when it gets going is very difficult to overcome and they were inspired.
"The World Cup is six months away in a neutral venue, it's a different thing."
And Johnson believes New Zealand remain the team to beat come September.
He added: "The All Blacks have been incredibly consistent for what seems like forever but all the rest of them, there's no guarantee that any of the other teams beat New Zealand on any given day.
"They're maybe not as clear as they were last year, but I still think they're the team in front and the ones to beat.
"Of the rest, Wales may have their noses in front, but these games are all on the moment.
The man set to replace Shaun Edwards with Wales
"You can be the best team in the tournament and have a bad hour and a half and you're going home.
"That's the best thing about it. You've got a chance. Back yourself as a team, make a difference and you've got a chance."
Martin Johnson was speaking as a Land Rover ambassador. Land Rover shares and understands the values of rugby. @LandRoverRugby
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