Australia Legend Shane Warne has told Alastair Cook that now is the time to prove him wrong and show his worth as England captain.

Warne has been critical of Cook's ability as skipper on several occasions in the past, but believes that now is the chance to hit back in the wake of Graeme Swann's controversial retirement from cricket with England trailing 3-0 in the Ashes ahead of two more Test matches.

"Out of all the years I've been watching England this is the most I've seen them in disarray. The wheels are off," Warne told Sky Sports News. "Now is a great opportunity for Alastair Cook to stand up and take charge and say: 'Right, guys. Enough is enough. This is what we're about, we're a good cricket side'.

"He needs to take charge. I think he hasn't taken enough charge in the whole series. If you rock up at the ground and look at the Australians, you know who's in charge.

"You look at the England team, and there's three or four players waving their hands around, telling people where they should be fielding. I just think Alastair Cook needs to take some charge and now's as good a time as any."

The fourth Test of the Ashes gets underway in Melbourne on Boxing Day.