Brendon McCullum has promised to use “a firm grip” to eradicate issues with alcohol and attitude among the England squad, admitting that “there were some mistakes made” by his players during last winter’s tours of New Zealand and Australia.

In his first interview since returning to England for the start of the international summer, with the first Test against New Zealand starting at Lord’s next Thursday, McCullum conceded that his team had proved unable to handle the pressure of an away Ashes series.

He also admitted that there had been “differences of opinion” with his Test captain, Ben Stokes, a player whose enjoyment in the game “may have just waned a little bit when we were in Australia”.

But despite calls for his removal after the team’s winter failures, the 44-year-old insisted he will be able to inspire the improvement necessary for England to win not just against this summer’s red-ball opponents, New Zealand and Pakistan, but also key series against India and Australia. McCullum was “confident that our best cricket is in front of us” and that he was “fiercely determined to try and make this cricket team a better version of what we are now”.

Speaking to the England and Wales Cricket Board in an interview that was published on its website, McCullum insisted of his squad that “fundamentally the culture of this group is really good”, but conceded there had been occasions when it lapsed.

“You’re bringing up young men, they’re in an environment where there is a lot of pressure, there’s lots of distractions,” he said. “They’re young guys who are growing up on the world stage under the brightest lights and sometimes they’re going to make mistakes.

“Ultimately your job as the leader of the organisation is to try to make sure that we aren’t making those mistakes because they’re not helpful. In an ideal world they would never happen. It’s not always an ideal world. We’re just going to make sure that we’re looking after these guys whilst also occasionally using a firm grip to ensure that we are not making those same mistakes again.”

McCullum said there had been no clear-the-air discussions with Stokes since the winter, because “there was nothing to clear the air about”, but the pair had had occasional disagreements. “There will always be differences of opinion, and that’s healthy,” he said. “That’s how in my opinion the best leaders work, they bounce off each other. In our own way, we’re trying to work out how to sharpen this thing so we become a better side.”

Stokes said the experience of England’s 4-1 Ashes defeat “hurts and sucks”, but McCullum said his captain had recovered from leading his team through a period of hugely disappointing failure. “There’s times when he doesn’t get everything right. No captain ever does,” he said.

“Sometimes it can be quite a lonely place. You’ve just got to make sure you’re always leaning into those around you who are there to support you and to help you. Stokesy will relish the opportunity he’s got in front of him and we’ll see him play with that real enjoyment which he’s had over the last few years, and which may have waned a little bit when we were in Australia.”

Jacob Bethell is expected to be fit to face New Zealand, though the injured finger that forced him to leave the Indian Premier League continues to be monitored, and is seen as a key part of what is, if not a new-look side, certainly a modified one.

“I hope you’ll see a lot of the stuff you’ve seen previously, with just a little bit of refinement, a little bit of sharpening,” McCullum said. “I think you’ll see a team play brave when it needs to, play smart when it needs to. A team which identifies moments where games can be won or lost and is able to win more of those than not.

“I’d like to see us just become a team that is feared by oppositions, not just for our knockout punch but our ability to jab as well. If we can do that, and we can box smart in any situation, in any conditions and against any opposition, and handle pressure when the pressure’s at its highest, then we will get the ultimate success.”