Powell came close to selection in the original squad

They are needed because of doubts about the fitness of Andrew Flintoff and Marcus Trescothick.

Clarke has made 16 one-day appearances for England, but it is Powell's first chance at international level.

If Trescothick is ruled out, he could make his debut in Thursday's day-night game against New Zealand.

Powell scored 49 for Wales against England in last Saturday's one-day challenge match at Cardiff.

It followed talks with chairman of selectors David Graveney, who told him he had been close to selection in the original squad.

CLARKE'S ENGLAND RECORD Tests: 2 96 runs (average 32.0), highest score 55, 4 wickets (average 15.0), best bowling 2-7 ODIs: 16 88 runs (average 9.7), highest score 37, 10 wickets (average 32.1), best bowling 2-28

The 27-year-old from Abergavenny has made 6,709 first-class runs at an average of 39 during his career, including 16 centuries.

"He's a very positive, aggressive batsman who has shown he can play in all forms of cricket.

"I think his best position is at three or four and if he gets an opportunity, I'm sure he'll grab it with both hands," Glamorgan coach John Derrick told BBC Sport.

Clarke, meanwhile, has been reprieved after struggling to make an impression during the winter tours to Bangladesh, Sri Lanka and West Indies.

He bowled tidiliy enough, taking seven wickets in nine games, but his highest score in five innings was only nine.

Flintoff is rated no better than 50-50 to play at Old Trafford on Thursday because of a foot injury, while Trescothick is suffering from a twisted ankle.

They are arguably England's two leading exponents of one-day cricket and if either are missing for the start of the series, it would be a major boost for opponents New Zealand and West Indies.

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"For every loss you get, you get an opportunity to play someone and give them a chance," said captain Michael Vaughan, who may open despite dropping to number four in the Test line-up.

"We've got to be pretty careful - we've got to look at the long-term and the summer we've got ahead.

"We definitely don't want to risk Freddie in a game and put him back a few weeks.

"If Tres doesn't make it, that will be a big loss. He's probably our best one-day batter - his stats would suggest that."

Vaughan is keen to see England identify - and stick with - a squad of about 20 players to carry the team through to the next World Cup in 2007.

"The sooner we get that, the better we will be," he said.

"Obviously we are trying to pick our squad to win every tournament that we are in, starting with this one, but the big one at the end of the summer is the Champions Trophy.

"I keep talking about building, but while you are building you can win games as well and it's a great opportunity for everyone in the squad to really make their mark on the game."