LOCK Dean Mumm insists there is plenty more to come from Australia’s scrum despite the Wallabies obliterating England at the set piece, writes Chris Kirwan.

The Aussies are tipped to have the edge on Wales in the tight in Saturday’s Pool A decider at Twickenham (kick-off 4.45pm) after doing a number on the tournament hosts last weekend.

That is amazing turnaround in fortunes for a nation that has traditionally has a soft underbelly with forwards coach Mario Ledesma, the legendary ex-Argentina hooker, rightly being given plenty of credit.

The perception of the Aussies as being a soft touch has changed but former Exeter lock Mumm says there is plenty more hard work to do.

“We've still got a way to go to be consistent and to be a great scrum you have to have that week in, week out,” he said.

“How we have improved the scrum so far is work. We have done a lot of work on it. We have had some reasonably simple focuses that Mario has worked on with us and the back room and the front five have worked really hard in every session.”

The Australia back will hope to once again be working off a solid platform but Wallabies coach Michael Cheika has some fitness worries.

Wing Rob Horne (shoulder) is set to miss out while full-back Israel Folau (ankle) is a doubt yet they still are able to call on replacements of the calibre of Toulon ace Drew Mitchell.

“I've only had that game against Uruguay, I'd love the opportunity,” he said. “But Kurtley Beale did well too when he came on (against England) and added some spark and injection from the back. “We've also got Henry Speight and Jo Tomane, so have a fair bit of choice there.”

Mitchell is back in the gold fold after the ARU relaxed its policy on picking players based overseas and, after a brace aginst Uruguay, has now scored more World Cup tries than any other Wallaby.

He is well placed to comment on how Cheika has turned the Aussies, who were in disarray a year ago, into the second favourites behind New Zealand.

"He's got everyone on the same page, playing for the right reasons and tapped into what it means to play for the Wallabies, who it is we are representing,” said Mitchell.