England were at rock bottom earlier this year following consecutive series defeats against Australia and West Indies, which led to Joe Root's resignation as Test captain.
The process began right after the 4-0 drubbing in the Ashes, when the management decided to axe Chris Silverwood and Graham Thorpe. Managing director Ashley Giles was also shown the door.
The England and Wales Cricket Board (ECB) decided to employ an out-of-the-box strategy by appointing two different coaches for red and white-ball cricket.
McCullum's arrival as Test coach received a mixed response from fans. However, the former New Zealand captain has silenced doubters with four consecutive wins under his belt, forging a formidable pair with skipper Ben Stokes.
Admitting his surprise with the instant success that the new-look England have garnered so far, Nasser Hussain wrote in his column for the Daily Mail:
"Clearly, these were very good appointments, but I don’t think any of us could have known quite how good it would be this summer and quite how rapid England’s improvement would be."
Adopting an aggressive brand of cricket, often dubbed "Bazball," the England side are out to rewrite the way the longest format is played. Several players have already benefitted from this unabashed style of play, with Jonny Bairstow emerging as the cream of the crop.
Bairstow has scored four centuries in his last five Test innings.
Noting that the revamped approach is not reckless cricket by any means, Nasser Hussain wrote:
"Root and Jonny Bairstow epitomise what this transformation of the England side is all about. Their approach is not about being reckless. It is not about swinging from the hip. It is a totally positive mindset with enjoyment of the game at the heart of it."
The Ben Stokes-led side marked the new era with a ruthless 3-0 clean sweep over New Zealand. They then chased down 378 runs against India at Edgbaston to cement the quality of their newfound approach.
"McCullum has ensured England are not fearful about the game" - Nasser Hussain
Apart from fuelling the team with aggression, McCullum has helped establish clarity in the dressing room. Stokes has established this as the key aspect behind each of their successful run chases so far under the former Kolkata Knight Riders coach.
Nasser Hussain believes England are not over-analysing like they used to before and added:
"McCullum has ensured England are not fearful about the game. They are not worrying about what’s ahead of them or over-analysing it."
"They are just strapping on their pads or getting a ball in their hands and going out and having fun. They have been reminded that playing for England is a wonderful experience, not something that should wear you down."
Following their resounding success against India and New Zealand, England will next host South Africa. The Proteas are currently placed second in the World Test Championship (WTC) standings.