Johnson can 'reopen' English scars - McGrath
Remarkable it may be to those who witnessed Johnson destroy England in Australia barely 18-months ago - when he claimed 37 wickets in the five Tests at an average of 13.97 - his place in the team for the first Test in Cardiff was suggested to be not entirely secure in the early stages of the tour.
Equally remarkably for those who saw the high standards reached by Ryan Harris in recent Ashes series, he is likely to struggle to make the first Test XI after missing the West Indies tour. Nothing better illustrates Australia's fast bowling strength.
But, as far as McGrath is concerned, Johnson is a "lethal" bowler and "can't be left out". Not only does he feel Johnson has developed into a more dangerous bowler than the one who has rarely fired on previous Ashes tours, but he thinks the psychological damage inflicted by Johnson in Australia gives him an advantage.
"The way he finished that last series in Australia was incredible," McGrath said. "He was player of the series without a doubt.
"There will be a lot of scars from that and if Johnson can get off to a good start here it will just reopen those scars. He will just power through.
"The first Test is a big game. If Johnson can have a good game and intimidate he is going to be lethal.
"They can't leave him out. Just because of the way he dominated in the last series and the way he bowled with good heat against Kent. If he starts the series well he won't stop.
"He hits the seam and if he hits the seam he is going to be very effective. When he came here last time his arm was lower and he wasn't hitting it so much.
"If he does well it will have a big effect on the rest of the team. It will really lift everyone. Test cricket is a psychological game and if you start well you go from strength to strength."
While McGrath remains an admirer of Harris, he suspects Australia will go into the first Test with Mitchell Starc and Josh Hazelwood as the first choice seamers and said he would prefer Shane Watson to Mitchell Marsh in the allrounder position.
"Harris is a quality player," he said. "But you don't want to leave out either Starc or Hazlewood and you have got to play Mitchell Johnson. So maybe they leave Rhino out.
"Hazlewood will enjoy the English conditions. I loved playing here with the Dukes ball. I think I averaged two wickets a Test more than elsewhere. He is the type of bowler who hits the deck and can swing the ball and he does it from a high action. I think he will really enjoy it.
"And I've always liked Watson. I think he has so much potential. He'll get given the opportunity to start and I want to see him go out there and perform."
McGrath predicting a whitewash has become a familiar pre-Ashes ritual. And he has not disappointed this time, either, though he did offer a few caveats. "When we came over here and we were playing pretty well there was never a 5-0 series win," he said. "But this could always be the first. I think everyone expects me to make a 5-0 prediction and I've dug a hole for myself over the years. If I say anything else they'll think I'm not confident."
But what may be more surprising is his suggestion that there should be a crackdown on sledging; at junior level at least. While insisting that the media tended to overplay the amount of verbal abuse occurring in Ashes series, he did concede that the behaviour of international sportsmen is often mimicked in clubs and playgrounds.
"To see kids sledging is totally wrong and should not be allowed," he said. "Unfortunately kids do copy what they see on TV. Sportsmen have a role to play as role models.
"But if I'm sitting there blaming someone on TV or sportsman for the way my children are playing then I'm not accepting responsibility and think that's pretty poor. For me as a parent I'm the role model for that child and the way they play the sport - have to take responsibility.
"It should never get personal or abusive. I didn't have any chat until I was well into my first-class career.
"But to be No. 1 you have to play hard. That isn't necessarily sledging. It's as much about body language than what you say. I don't want to see a bunch of robots and a bowler clapping a batsman after he's been hit for four and saying good shot. Just play it hard and tough. That is why the umpires are there and the match referee is there."
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George Dobell is a senior correspondent at ESPNcricinfo