Ashes 2015: Mitchell Johnson as fast as ever - Michael Clarke

Mitchell Johnson was not part of the Australia squad beaten in England in 2013

Australia captain Michael Clarke says pace bowler Mitchell Johnson is ready to have a "huge impact" on the Ashes, which begin on Wednesday in Cardiff.

Johnson took 37 wickets in Australia's 5-0 win of 2013-14, but averages 37.73 with the ball in England.

"He's bowling as fast as I've faced in the nets, but the harder thing is that he's swinging it," said Clarke.

"People doubt how well he can bowl in these conditions, but that has given him that fire in his belly."

Australia have not won in England since 2001, with 33-year-old left-armer Johnson part of the 2009 squad that was beaten by England after playing two Tests against Pakistan in the UK.

And after the home Ashes defeat of 2010-11, when he was ridiculed by England's travelling fans, Johnson's pace terrorised the tourists three years later as he was named man of the series.

"When he sees a big series or a big opportunity, he really looks forward to it," added batsman Clarke. "He's fit, healthy and excited about what lies ahead.

"If he can bowl the way he's bowled since we landed in this country, he can have a huge impact."

However, captain Alastair Cook, looking to lead England to their fourth Ashes win in five series, says his side must focus on their previous successes against Johnson and Australia.

"Mitchell was outstanding in that last series, but we had the wood over him in 2009 and 2010-11," said opening batsman Cook, 30. "I genuinely believe this series will not just come to down to the performance of one bowler.

"The last Ashes series has gone, we cannot keep harping on about that. Five months before that, we won the Ashes 3-0 in our own conditions.

"We have to be very careful not to read too much into that because this is a brand new challenge and a fresh start."

Neither captain was prepared to reveal his team for the first Test, with both saying the respective sides will be confirmed at the toss.

England have included leg-spinner Adil Rashid in their 13-man party, but wet weather has made his inclusion for a Test debut less likely.

Clarke, 34, said the presence of grass on the Cardiff wicket could lead to Australia leaving out spinner Nathan Lyon in order to play four frontline pace bowlers.

He also expects England to field the same XI that drew 1-1 with New Zealand earlier in the summer.

"There's a chance we will play four seamers, there was certainly more of a chance yesterday when we saw the grass on the wicket," said Clarke. "It might have changed a little bit today and that is why the selectors are waiting to see the conditions.

"I think everybody knows the England team, I don't think that 11 will change. They will stick with who played in the Tests against New Zealand."

England (from): Alastair Cook (Essex, capt), Adam Lyth, Gary Ballance (both Yorkshire), Ian Bell (Warwickshire), Joe Root (Yorkshire), Ben Stokes (Durham), Jos Buttler (Lancashire, wk), Moeen Ali (Worcestershire), Stuart Broad (Nottinghamshire), Mark Wood (Durham), James Anderson (Lancashire), Adil Rashid (Yorkshire), Steven Finn (Middlesex).

Australia (from): Michael Clarke (capt), Steve Smith (vice-capt), Fawad Ahmed, Brad Haddin (wk), Josh Hazlewood, Mitchell Johnson, Nathan Lyon, Mitchell Marsh, Shaun Marsh, Peter Nevill (wk), Chris Rogers, Peter Siddle, Mitchell Starc, Adam Voges, David Warner, Shane Watson.