Cooley has played a key role in England's resurgence

Cooley, who has been praised for his work with England's pace battery, is set to take up a similar job in his native Australia in May 2006.

Fletcher said: "It is very disappointing to lose a person of Troy's calibre.

"We have worked hard to build the ideal management team so to lose a pivotal figure is a great shame."

Cooley joined England in 2003 and has been hailed as the man who developed the talents of Matthew Hoggard, Steve Harmison, Andrew Flintoff and Simon Jones.

Masterclass: Troy Cooley on reverse swing

England's focus on reverse swing was a key element of England's Ashes triumph.

"The decision to return to Australia was the hardest career decision I have ever had to make," said Cooley. "My current appointment is very much my dream job.

"My decision to return to move on in May is entirely due to my desire to return to Australia with my young family and my having been offered a similar role with my home country."

He insisted that he felt no divided loyalties during the Ashes, having worked in tandem with the England attack for some time.

"There was a lot of hard work going into what we've done over the last three years," he said.

"You really get tied up with the team that you're working with, it's a very close team and being part of it was very exciting."

It's a big blow for us. He's been a part of our young guys becoming a good bowling unit Marcus Trescothick

Cooley will have six months to work with the Australian team ahead of the next Ashes series against England in December 2006, and England's chairman of selectors David Graveney admitted "it's a significant blow".

Cricket Australia chief executive James Sutherland said: "Troy was our first choice, the players rate him highly and his work in England speaks for itself.

"We're delighted he's agreed to take on this important role as we move ahead with our plans for the Ashes here in 2006-07."

Cooley and former Australia wicket-keeper Rod Marsh helped set up the fast bowling programme at England's National Cricket Academy.

Acting England skipper Marcus Trescothick admitted that the loss of Cooley would be difficult for the team.

"It's a big blow for us," he said. "He's been with us for the good times we've had since we've really picked our cricket up.

"He's been a part of our young guys maturing and becoming a good bowling unit.

"It was probably only a matter of time with him coming from Australia that he would go back but I didn't realise it would happen this quickly.