Harmison successfully appealing for an lbw at Worcester

Harmison came in for heavy criticism for his performances during England's 5-0 hammering by Australia last winter.

He then announced his retirement from one-day international cricket.

But he collected eight wickets in a Championship win over Worcestershire and Cook said: "Steve has been terrific for the last three weeks."

The first ball of the 2006-07 Ashes series, bowled by Harmison, was so wide it was taken by Andrew Flintoff at second slip.

The 28-year-old, a former world number one bowler, ended up with 10 wickets in the series, each costing 61.40 runs.

But Cook said: "We went off to South Africa pre-season and he threw his lot in there and his bowling is coming on now.

"He is getting back to the relaxed fellow he was when he first joined us.

Emotionally he is getting ready to play Test cricket again Geoff Cook

"He enjoys playing for Durham and he is starting to get towards Test match standard with the ball now.

"He is a world-class bowler and, when we played Worcestershire last week, he was really the difference between the two teams.

"It is not pleasant for the opposition when he is playing for Durham - but it is pleasant for our lads to have his presence in the team."

Cook also believes that Harmison will put the stick he received behind him as England look to rebuild and regroup after a disappointing six months.

He said: "Steve is a sensitive guy and he is the same as anyone in that, if you get stick it is not pleasant, but he has bounced back.

"Emotionally he is getting ready to play Test cricket again."