Kevin Pietersen has thrown a metaphorical hand grenade into England's dressing room ahead of Thursday's third Magellan Ashes Test – openly questioning Alastair Cook's future and accusing the tourists of looking "scared" whenever they face Australia's bowling attack.

Pietersen, sacked after England were whitewashed on their last Ashes tour in 2013-14, also criticised captain Joe Root's failure to lead from the front with the bat during the first two Tests and hinted at possible disharmony within the current set-up.

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However, it is Pietersen's scathing verdict on Cook, England's all-time leading Test runscorer and century-maker, that was most striking.

The third match of this series at the WACA, starting on Thursday, will be Cook's 150th Test appearance.

However, referencing comments from former Australia captain Ricky Ponting before the series began that Cook would struggle after giving up the captaincy earlier this year, Pietersen says his former team-mate, who has scored 62 runs across four innings in this Ashes so far, looks like he has lost interest in playing.

The South Africa-born batsmen said: "I don't know if he can turn things around. Ponting talked about it before the series saying he's going to find it very difficult after getting rid of the captaincy to get himself up and turn it around.

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"Ponting's been through it, he's done it all before. He's played 168 Test matches and he calls things pretty accurately and pretty well and it looks like Cook is not very interested.

"Just the way that he's got out, the manner of his dismissals and also the way he's walked off the field once he's got out. That's the sign of a bloke who goes, 'You know what, maybe my time is up'.

"He might be able to put up a performance in his 150th Test match. He's got a Test hundred at the WACA before. But who knows?

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"That fire burns in your belly for a number of years and then eventually it starts to go out. I had spotted it before the series and there's certainly no signs at the moment to prove there's any fire in Cook's belly."

Pietersen, who averaged 45.76 in 15 away Ashes Tests, also accused England's batsmen of being timid and looking scared against Australia's pace attack of Mitchell Starc, Pat Cummins and Josh Hazelwood.

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Speaking on behalf of UK Ashes broadcaster BT Sport, Pietersen said: "There's no drive, there's no real determination to say, 'Well, these Australian bowlers are not bowling 100 miles an hour'.

"They're not bowling at a speed they haven't faced throughout their careers. One or two balls have been 150kph but they're in the 140s, which isn't something that people haven't faced before.

"So to me it looks like the England batters are making out that this Australian bowling attack in their head is some of the fastest they've ever faced, is the scariest bowling they've ever faced and it looks like they're just very nervous when they go out to bat.

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"It's frustrating as a commentator because I want to see somebody try to get on top of the Australian bowlers. That's what I did in my career. I was like, 'The quicker you come, the quicker you're going to go'. And even if I didn't feel good on occasions I made it look like I felt good because that's what you need to do in Australia.

"You need to get on top of them and you need to show them that you're not scared and you're not worried and there's no-one in that England side at the moment that doesn't look scared. And that's my issue, that's the concern."

There were also harsh words for Root, who has failed to convert two half-centuries so far in this Ashes series and was upstaged by a brilliant hundred from opposite number Steve Smith in the opening Test at the Gabba.

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"Joe Root hasn't set the world on fire at all, absolutely not by any stretch of the imagination," said Pietersen. "So it's not as if we're going to blame everyone else. You need to lead from the front in Australia."

Asked about whether this England team look like they will also be beaten 5-0, Pietersen said: "There are signs with the way that the guys capitulated on the last day of the last two Test matches that, unless they really start well in Perth, then it could happen.

"But this Australian side isn't as good as some of the Australian sides England have played in Australia.

"I don't know how the team operate and I don't know [coach] Trevor Bayliss. We fell apart [in 2013-14], there was just a strained relationship in our dressing-room from the coach downwards. That played a big, big role in what happened.

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"But I think Bayliss seems very relaxed and chilled and so does Root at the start of his captaincy career.

"I have heard there are rumours that a couple of people didn't want to bowl first in Adelaide [after Root won the toss and did just that]. If a couple of people didn't want to bowl and Root's made that decision and they've lost, yeah there are certain factions that can happen in dressing-rooms when that happens.

"We'll just have to wait and see. I think Perth is going to be a fascinating Test match – to see if the wheels are going to come off or not."

2017-18 International Fixtures

Magellan Ashes Series

Australia Test squad: Steve Smith (c), David Warner (vc), Cameron Bancroft, Usman Khawaja, Peter Handscomb, Shaun Marsh, Mitchell Marsh, Tim Paine (wk), Mitchell Starc, Pat Cummins, Nathan Lyon, Josh Hazlewood, Jackson Bird.

England Test squad: Joe Root (c), James Anderson (vc), Moeen Ali, Jonny Bairstow, Jake Ball, Gary Ballance, Stuart Broad, Alastair Cook, Mason Crane, Tom Curran, Ben Foakes, Dawid Malan, Craig Overton, Ben Stokes, Mark Stoneman, James Vince, Chris Woakes.

First Test Australia won by 10 wickets. Scorecard

Second Test Australia won by 120 runs (Day-Night). Scorecard

Third Test WACA Ground, December 14-18. Tickets

Fourth Test MCG, December 26-30. Tickets

Fifth Test SCG, January 4-8 (Pink Test). Tickets

Gillette ODI Series v England

First ODI MCG, January 14. Tickets

Second ODI Gabba, January 19. Tickets

Third ODI SCG, January 21. Tickets

Fourth ODI Adelaide Oval, January 26. Tickets

Fifth ODI Perth Stadium, January 28. Tickets

Prime Minister's XI

PM's XI v England Manuka Oval, February 2. Tickets

Gillette T20 trans-Tasman Tri-Series

First T20I Australia v NZ, SCG, February 3. Tickets

Second T20I – Australia v England, Blundstone Arena, February 7. Tickets

Third T20I – Australia v England, MCG, February 10. Tickets

Fourth T20I – NZ v England, Wellington, February 14

Fifth T20I – NZ v Australia, Eden Park, February 16

Sixth T20I – NZ v England, Seddon Park, February 18

Final – TBC, Eden Park, February 21