A relentless Australia spearheaded by debutant Scott Boland skittled England for an embarrassing 68 on Tuesday to win the third Test by an innings and 14 runs and retain the Ashes with two matches still to play.

Just when a demoralised England thought their tour could not get much worse, they folded in the morning on day three in Melbourne and will now be desperate to avoid a series whitewash.

England resumed at the MCG on 31 for four, still 51 runs behind, after a disastrous final hour on Monday against some outstanding fast bowling that left their Ashes dreams in tatters.

Their survival rested on skipper Joe Root, but when he fell for 28, it was just a matter of time before the rest followed -- all over before lunch in an embarrassing chapter for English cricket.

Boland, called up as injury cover, was invincible on his home ground, taking 6-7 off four overs, equalling the record for the fastest five-wicket haul in 19 balls.

Mitchell Starc ended with 3-29 as England's misery was complete.

"It is pretty insane. Just an awesome few weeks, everything clicked and everything worked out," said Australian skipper Pat Cummins. "Thrilled for Scott Boland. We have been relentless.

"The bowlers have just turned up and owned their areas outside off-stump. There have been big partnerships, everyone's performed, everyone's contributed -- it's a great feeling."

Ben Stokes resumed on two but his poor tour continued when he was clean-bowled by Starc for 11. Jonny Bairstow made five and when Root was out it was all over, with the tailenders quickly following.

"It is what it is," said a dejected Root, who is facing growing calls over his captaincy.

"Credit to Australia, they blew us away last night and they have outplayed us in this Test match -- in fact the series so far.

"We have a lot of hard work to do now and come back strong in the last two games."

Covid threat

Whether there would be play at all at the MCG was in doubt after four members of the England party -- two support staff and two family members - tested positive for coronavirus on Monday.

But all players from both teams underwent PCR tests after stumps and returned negative results Tuesday morning, with the first ball bowled on schedule.

England had headed to Melbourne knowing they must win to keep the five-Test series alive after heavy defeats in Brisbane and Adelaide, with Australia only needing a draw to retain the urn as holders.

And they fleetingly hauled themselves into contention on the back of a vintage bowling effort from veteran seamer James Anderson, which restricted Australia to 267 in their first innings in reply to the tourists' 185.

It was only an 82-run lead but any dreams England had of staying in the Test -- and the series -- fell apart in the face of an intense fast-bowling blitz on Monday from Starc, Cummins and Boland.

In an hour of mayhem, they removed hapless openers Zak Crawley (five) and Haseeb Hameed (seven), Dawid Malan for a golden duck and nightwatchman Jack Leach (0), leaving England staring into the abyss on 31 for four after another stunning collapse.

"I'm speechless," said Boland, the debutant and England's tormentor-in-chief.

"Coming here today, I thought we had a pretty good chance of winning, but I had no idea it'd be over before midday."

‘Clueless’

Once again, England's hopes had rested with Root, who resumed on 12, and star all-rounder Stokes.

Stokes has failed to fire but he flogged Starc for four to show intent, only for the New South Welshman to respond in devastating fashion two balls later with a fuller, tighter delivery that clattered into the stumps.

Root took a nasty blow in the groin area off Cummins on 23 and eventually went for 28, caught by David Warner at slip off Boland.

Despite the dismissal it capped an incredible 12 months for Root with the bat, ending the calendar year with the third most Test runs (1,708) in history, surpassed only by Pakistan's Mohammad Yousuf (1,788 in 2006) and Viv Richards (1,710 in 1976).

England's miserable batting, which followed eerily familiar collapses in Brisbane and Adelaide, was castigated by the British media.

"Gutless England batsmen deliver full spectrum of ineptitude," screamed The Daily Telegraph, while The Sun slammed "Clueless England".