By Martin Gough BBC Sport at Lord's

In May 2000, England selected a 21-year-old, inexperienced Steve Harmison in their squad for the first Test of the summer against Zimbabwe at Lord's.

Harmison has yet to better his debut three-wicket haul

But it would be another two years before the Durham pace bowler made his Test debut, and another year before he would be regarded as an automatic choice.

The selectors were justified three years ago when their choice of Ed Giddins' swing reaped figures of 5-15.

But while Giddins is now with his fourth county, struggling to make regular appearances in the Championship, Harmison is preparing again to take on Zimbabwe.

"A lot of water has gone under the bridge between then and now," Harmison told the BBC Sport website.

"In 2000 I believed I wasn't good enough to play Test cricket - if I was good enough to play in that game I would've played but it wasn't my time."

That it took two years to take the next step up is largely down, he says, to injuries at the wrong time.

His back, shins and side have all proved troublesome, usually flaring up in the week leading up to the announcement of a Test squad.

And he is still far from the finished article, as the Northumberland-born bowler is the first to admit.

I had a few ups and downs - some more traumatic than others - but that's what life is all about Steve Harmison

For all his bat-jarring pace and bounce, Harmison is a low-key character.

His Test debut at Trent Bridge brought five wickets in a drawn match, but he quietly impressed rather than entering in a blaze of glory.

Since then there have been highs and lows to his international career.

The highs have yet to be that high, his debut three-wicket haul matched only once, at Sydney, when he was part of England's consolation Test win.

The lows have been ankle-level and very public, like the opening match of the Ashes tour, where he sustained a concussion and went on to bowl seven consecutive wides in a single over.

So, for a man billed as introverted, it is a surprise to hear him claim he would happily do it all again.

"They're the best side in the world and you always want to play against the best. I enjoyed the challenge - I'm someone who likes a challenge," he goes on.

Harmison's failures in Australia were in the full public glare

"To play against Steve Waugh, Justin Langer, Ricky Ponting, to play in front of 30,000 people; that's where you want to be.

"I've always been the same. I wouldn't say shy; I just keep myself to myself. I don't like the publicity; I just want to get on with it."

Harmison's continued Ashes contribution had a lot to do with the perseverance of captain Nasser Hussain and coach Duncan Fletcher, bringing a continuity once not seen in England selection.

"You've got to back your players and you've got to be loyal to them. It's the only way they're going to perform for you."

"I see that a lot in our management - if players have a bad day they have a bad day but it isn't held against them.

Harmison is anxious not to be seen as disrespectful of Thursday's opponents, but still believes England will look far better in comparison to a team other than Australia.

"Zimbabwe are always a good fighting side and they've got some good players," he says.

"But I believe if we played any of the other Test nations the way we played our cricket in the winter we would have beaten most of them."

With injuries cutting a swathe through England's pace corps, they now need Harmison to take a further step in his development, whatever the quality of the opposition.