"'If in doubt, always take the aggressive option' is one of our big catch-cries. I make sure I play with a full heart and no fear, just go out there and try and take games by the scruff of the neck."
That aggression has paid off and, conversely to their child-like enthusiasm, McCullum acknowledged that he and his teammates has "grown up a lot" since they were last in England.
"How we were viewed two years ago was that we were overpaid, under-delivering prima donnas, and a lot of that was fair," McCullum said. "We hit rock bottom but that allowed us to strip everything out and plot a pathway forward.
"One of the things that we decided we had to change was the public perception of us as people, not just on the cricket field but off it as well. The changes we have made have endeared us to our public and let's hope that continues for a long time."
Of course, a change in attitude is rendered irrelevant without results. Those have arrived, most notably at the Cricket World Cup, and tomorrow night will mark New Zealand's first action since being defeated by Australia in the final in March.
Despite their success at that tournament, capturing the nation's attention with several thrilling displays, McCullum was pleased to again be donning the whites for a format he called the pinnacle of the game.
"It's sacred, it's something that you've got to try and protect and that's where our motivation is," he said. "It has to hold priority. It's the toughest challenge. You fail more times than you succeed in test cricket, but when you do have success you know that you've had to earn it."
McCullum hoped his charges would earn another positive result from the two-test series, a contest that he thought pitted together two quality squads.
"England are stacked full of good players. They've got an exceptional character as captain. I think Alastair [Cook] is a wonderful player, he's gone through a pretty tough time of late, but he bounced back with a hundred not long ago and that just shows the character of the man.
"But we've played some really good cricket over the last 12 to 24 months - we've progressed up the rankings, which was no easy feat considering where were 24 months ago. I know we'll compete and we've got a good opportunity."