World Cup-winning captain Martin Johnson insists the path for England, Australia and Wales to the knockout stages of this year's tournament is the toughest in history, and believes the Wallabies are the most dangerous team on the planet.
The enormity of the challenge facing the tournament hosts, England and Wales, in Pool A was laid bare last week following the Wallabies' Rugby Championship title triumph and Fiji's success in the Pacific Nations Cup.
On three consecutive weekends, England must dispatch Fiji, Wales and Australia if they are to be offered a route through the less arduous half of the World Cup draw, avoiding New Zealand and South Africa.
Whoever does advance into the knockout stages, Johnson believes they will benefit from having been battle hardened against high-calibre opposition.
"It's the toughest pool there has ever been in a World Cup and someone will be going home early," Johnson told Press Association Sport.
"Whoever loses England v Wales, their next game becomes a must win. They'll have to beat Australia just to stay in the tournament.
"But in a way it won't do England any harm at all. It's often the teams that have to fight and battle who will be in the best position come the end of the World Cup. If they win the group then it doesn't really get any harder, at least until the final."
Australia's visit to Twickenham on October 3 is already looming large, with England forwards coach Graham Rowntree revealing on Tuesday that 'we're watching them constantly as a group, that country are going places'.
Johnson, captain of the England team that won the 2003 World Cup following a 20-17 victory over the Wallabies in the Sydney final, views them as the most dangerous team on the global stage.
"Australia can be utterly lethal when it comes to scoring tries out of situations where there's nothing on, more so any other team in the world," Johnson said.
"They execute with their hands very, very well and suddenly they're in. They score tries and that makes them lethal.
"People perceive they have weaknesses here and there, but they're usually able to cover them up. They almost won a World Cup in 2003 when they couldn't really scrummage.
"If England get ascendancy in the scrum and the referee penalises Australia, it makes a big difference to the game. If he doesn't penalise, then it nullifies the advantage at the scrum."