Last year, when Alastair Cook was being taken to some dark places by the game of cricket, I dropped him a quick text message - just as a show of support, from one captain to another.

No one who has played the game can honestly claim they haven’t been in those places themselves.

I’ve always admired Cook’s toughness and I get on well with him. But not all captains around the world are bosom buddies. I wanted to pass on a simple message: tough times don’t last, but tough blokes do. He responded to my message and we’ve exchanged a few since. We also bonded earlier in the summer when both our sides were trying to play an exciting brand of cricket during our drawn Test series.

So to see him emerge from those low times and captain England to an excellent Ashes victory is a real thrill. I’m delighted for him.

Alastair Cook has emerged from a dark period as England captained and shown his toughness in the process

Cook celebrates England's victory over Australia at Trent Bridge that earned them a 3-1 Ashes series lead

New Zealand captain Brendon McCullum tells Sportsmail he has been in touch with Cook during his turmoils

I’ve captained New Zealand in two Test series against Cook’s team and it’s fair to say he changed a bit in the meantime. The first series was back home in the early part of 2013 when he had only recently inherited the side built by Andrew Strauss and Andy Flower.

There were some outstanding individuals in that team but some were nearing the end of their careers and it didn’t yet feel like Cook’s dressing-room. Captaincy is about more than taking the field with a bunch of talented cricketers.

But by the time we toured England earlier this summer I could see the change. He looked like he had taken on board some of the criticism that had been thrown his way, which is always a good sign in a leader, and had persuaded his team to join him for the ride. Watching him during this Ashes series, he’s gone even further. He seems content with his standing and comfortable with the style of play England have adopted. He’s quite clearly the leader - and his players are only too happy to follow.

Some people might think it’s all down to the new coaching structure, and there’s no doubt that Paul Farbrace, who was in charge against us, and Trevor Bayliss have helped encourage England’s youngsters to play with freedom. But in my experience it’s not possible for a team to adopt a style of play unless the captain is 100 per cent behind it - and unless the team fully respects the captain. You can have all the plans in the world but it’s up to the captain to get his players to buy into a new philosophy. Otherwise, forget it.

Cook can take tremendous satisfaction from the way the likes of Joe Root, Ben Stokes and Moeen Ali have adopted that positive style. It may not be a style that suits Cook himself as a batsman but that doesn’t mean you can’t deliver the message to the team. And being positive can mean a variety of things. In Cook’s case, it means following through with the cricket that feels most authentic to him.

McCullum (second left) celebrates the wicket of Cook during their Test at Eden Park, Auckland, in March 2013

England's players have rallied around Cook during the difficult period leading up to and during the Ashes

His nine-hour 162 against us at Lord’s earlier in the summer was a classic example. Stokes batted brilliantly for his hundred in that innings but without Cook’s solidity at the other end it might not have been possible. When he’s in that mood with the bat he can be a real pain in the backside. With most guys, you feel you can always stay in the game by rolling out different plans — some bouncers, a seventh-stump line or dragging him across his stumps, then aiming straight for an lbw. But Cook doesn’t bite. He’s got a great defence and just wears you down.

That Lord’s innings was England’s captain at his most authentic and I hope he doesn’t deviate from that as his side move forward with their brand of cricket.

Captaincy is a different matter. Against Australia, Cook has looked more aggressive and more innovative than before. He’s making proactive decisions.

Sometimes when you’re behind in a game you have to bluff a bit to make the opposition feel under pressure. He looks like he’s willing to do that now. Sure, he’s had the bowlers and conditions to back him up, but you’ve still got to be able to implement a strategy.

Cook leaves the field during a marathon century against the Black Caps in May that epitomised his captaincy

England have a couple of tough tours coming up, to the UAE and South Africa, but I believe they can prosper overseas. The UAE is a hard place for visiting sides. You have to make sure you use the new ball well, then bring your spinners into the game, but England have the batsmen to score runs out there. Once you do that, you’re in with a chance.

Australia face another challenge now that Steve Smith is set to replace Michael Clarke as captain. He’ll have his work cut out because they look set to lose a few players and he’ll have to balance his desire to stamp his mark on the team with the need to get results.

The Aussies have always produced talented cricketers. It’s just a question of getting them in the right seats on the bus - something I don’t feel they’ve done that well during the Ashes. But they’ll find a way. They usually do.

As for Clarke, I was surprised by the timing of his decision but I’d rather focus on what a wonderful player he’s been. He was one of the first rock-star cricketers but he backed that up with his runs.

Not many players get to make an impact over such a long period and he can be very proud of his career. It’s always disappointing when a world-class performer leaves on a low but he’s not the first player to discover that sport rarely contains a fairytale ending. I wish him the very best in whatever he does next.