ENGLAND will be "brutally honest" when they ask tough questions about personnel and methods after their heavy defeat in this winter's Ashes.

Assistant coach Paul Farbrace spelled out, with England digging deep during day four of the final Test in Sydney to try and avoid a 4-0 defeat, that all players and staff must be prepared for some straight-talking.

No-one, it seems, will be off limits – although Farbrace was at pains to stress that captain Joe Root has been an impressive cornerstone in England's tightest spots in Australia and will go on to be a "very good captain" of his country.

Australia piled up 649-7 declared as brothers Shaun and Mitchell Marsh completed centuries – 156 and 101 respectively – before Root stood firm for an unbeaten 42 out of 93-4 at the close.

Still 210 runs adrift, the tourists' slim chances of avoiding an innings defeat rested on their captain's shoulders.

Acknowledging England have made a habit of conceding 600-plus totals away from home of late, Farbrace said: "There is (a problem).

"We haven't been good enough to put Australia under pressure, then you're constantly chasing the game and you make it very hard for yourself."

A tough series debrief is inevitable and Farbrace added: "When you come away from home, it does expose issues you have in your team.

"We have a choice. We either say 'we've had some really good positives' or we are actually honest and say 'there are certain areas that are not good enough and we've got to do something about it'.

"That's every single one of us. Everybody needs to look very closely and say 'have we got the right people in the right places and are we doing the right things?'.

"The key is how honest you are. Sometimes those tough conversations have to be brutally honest.

"If England are serious about coming back here and winning in four years' time, the planning needs to start in the next couple of days."

Their frailties have been laid bare in Sydney and Farbrace reflected: "In many ways the last few days have summed up our trip. It's been exceptionally tough.

"But the one thing we've talked an awful lot about is just making sure we keep battling. Sometimes, when you're out-skilled, all you can do is keep fighting; keep scrapping."

Root is less than a year into his tenure and Farbrace is confident the Yorkshire batsman will "definitely" be all the stronger for this winter's tough tour.

Farbrace said: "He is very determined. We've seen in the dressing room, the way he leads, speaks, the way he is around the team, that he is growing into and going to become a very good captain.

"He'll have learned a lot in this series, a lot in his short time as England captain, and he will only get better for that experience – because that is the nature of the person."

Australia had yet another dominant day. The nearest they came to a blip was when the Marsh brothers forgot, during their mid-pitch hug to celebrate Mitch's century, that they needed to complete the two runs.

Shaun Marsh, the elder, said: "That was my fault. Emotions got the better of me and I just wanted to give him a hug. I saw him starting to celebrate and lost all concept of where the ball was."

Little brother Mitch added: "I pretty much went for the high-five and Shaun went for the hug. We parked in the middle and (then) had a quick split-second of panic."

There have been precious few of those for Australia this winter.