The Ashes 2023: Stuart Broad continues to improve and is not finished yet - Jonathan Agnew

Stuart Broad reaching 600 Test wickets is an extraordinary achievement.

You go back to the fresh-faced youngster who made his debut in a broiling hot Test in Colombo and didn't take his first wicket - Chaminda Vaas - until the 147th over as Sri Lanka scored millions of runs.

Here we are 599 wickets on after he dismissed Australia's Travis Head on day one of the fourth Ashes Test at Old Trafford.

It's remarkable really.

What I always think about Stuart's bowling is how much better he's got. He looked promising when he started but not in the way Jimmy Anderson looked promising.

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There have been times in Stuart's career where you're not entirely sure what he's supposed to be bowling.

Is he supposed to be bowling quick, all bouncers and aggression, or is he someone who pitches it up and tries to swing it?

What he has done is manage to keep learning new skills and get better all the way through his career. Bowlers do improve but his rate of improvement has been really sharp.

He came to bowling late, only really starting when he was 14 or 15. He used to be a batsman.

He's kept developing even up to the start of this series when he learnt to bowl an out-swinger. That's a new development.

I know how hard he works. There was a time when he wasn't happy with his wrist position and he'd bowl for hours and hours at the indoor school at Trent Bridge. You only get to be that good by hard work and practice.

I've known Stuart since he was a very young lad and this will be huge for him. It's a massive achievement.

I'm president of his club Egerton Park in Melton Mowbray where he started and I know how thrilled they'll all be.

Years ago, they sent this young boy away to Australia for the winter, he came back and no-one recognised him because he'd grown about six inches! They're very proud of him.

The Broad family are extraordinarily grounded. Stuart's mum was at Old Trafford on day one and didn't know he had 598 wickets. That's just the way they are. It's absolutely wonderful she was here to see his 600th.

Stuart deserves a massive amount of respect for the way he's worked at it and the challenges he's faced along the way.

Four years ago, he didn't think he'd get through that Ashes series.

I know he was thinking about what he should do career-wise because he thought that if he got dropped from the team that summer then he wouldn't get back in again.

That was 160-odd wickets ago. He was so determined he would not be dropped.

He almost used that as the driving force - that refusal to concede he might finish there and, of course, he didn't and he's gone from strength to strength.

Broad has judged his preparation for this series really well and I know he's very happy with how he's bowled. He's got a great rhythm and has hardly bowled a bad spell.

That first pitch at Edgbaston was a horrible thing for someone like him to bowl on and he had a good chunter as he does.

That's one of the things I always love about Stuart. When he's on a flat pitch or things aren't going very well, he deliberately makes himself angry.

He'll target something - or somebody - totally inoffensive and get in a lather about it.

At Lord's, he got himself cross about the unusual lines an Australia bowler had marked for his run-up and insisted on the groundsman coming out and painting over them.

Ridiculous, really, but it fires him up.

Fast bowlers need that because it is hard work and you're bowling long spells. Bowling at this level, you can't coast.

Every spell has to be incisive and meaningful so Broad will pick on something just to make the juices flow.

That's why Ashes series bring out the best of him.

He knows all about the rivalry, he understands it and he revels in it. I don't think it's any coincidence he's at his best when playing Australia.

Indeed, he's now taken more wickets against Australia in Tests than any other player.

The motivation now could be to see if he can keep going and surpass Anderson, who has 688 wickets. It'll be very interesting to see what happens with those two.

There was a time a few years ago where I think they had in their mind an image of walking off at The Oval together at the end of a series.

I don't know how long they'll go on for but I think we'll see Stuart bowling for a while yet.

Jonathan Agnew was talking to BBC Sport's Sam Drury.