England had won only one of their previous 17 tests when the new leadership, including Key himself, was put in charge to script a turnaround.

England have since blanked world test champions New Zealand 3-0 and beat India in Edgbaston, particularly impressive was how they chased down 270-plus targets in all four matches.

"I never thought it would work like this," Key told BBC Test Match Special.

"There will be times when it won't work, but for now it's been fantastic to see."

Key, however, felt the term 'Bazball' did not do justice to the hard work put in by McCullum and Stokes.

"I'm not mad on Bazball the phrase," he said.

"It's not something I particularly enjoy because it devalues what Ben and Brendon have done."

Key said appointing McCullum was a gamble considering the former New Zealand captain had no red ball coaching experience before taking up the England job.

"I saw it as though I had two choices," Key said.

"Did the England team, the test team in particular, need someone who was going to be like a drill sergeant, a real hard taskmaster who's going to be really tough on them and try and drive them in that way?

"I felt they needed someone to just take the pressure off them a little bit.

"I wanted someone who, with the talented players that we had, just freed them up a bit and got them out there to be the best players they possibly can be."

England now have a break from test matches with white ball cricket taking centre stage. The ODI side beat India by 100 runs on Thursday, with Reece Topley (28) setting a new record for best figues by an England bowler in ODIs with 6-24. 

Their next test match comes in August with a three-game series against South Africa.