Beauden Barrett is still cutting his baby teeth as an international No 10.

He may be World Rugby's player of the year for the last two seasons running, and short-listed for the award again this year, yet All Blacks coach Steve Hansen believes Barrett is still unravelling the secrets on what it takes to be a five-star international first five-eighth.

GETTY IMAGES Beauden Barrett has played 70 tests for the All Blacks, but his transition to being a regular starter at first five-eighth didn't start until 2016.

Given he has collected 70 test caps since 2012, and been a regular starter at No 10 since being preferred ahead of Aaron Cruden in 2016, Barrett would appear to most people to be near the peak of his game.

Hansen, who has named Damian McKenzie at fullback to assist Barrett in the playmaker's role for the test against England, isn't subscribing to that view.

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Speaking ahead of the match at Twickenham on Sunday morning, Hansen reflected on Barrett's slow progression towards being the All Blacks' top-ranked No 10 and said he's still learning the finer points of the complicated job.

"When he first came on to the scene, he was that second driver," Hansen said. "He would come on and play at fullback. Him and Dan (Carter) operated pretty well together.

"I remember a game in Wales where he did it and turned the game around. At the Hurricanes, they don't have the same luxury of having two drivers and I would say he has found at times he has been a bit frustrated there.

"So it's a learning curve for him as a player. And he is still his infancy as a five-eighth, we tend to forget he hasn't really been there for a long time in his career. Four years isn't a long time."

Barrett has been prepared to play the long game. His progression has involved being used off the bench as a fullback, and slowly being exposed to the job at first-five until landing the role fulltime after the 2015 World Cup.

AP Richie Mo'unga crosses for a try against Japan during the test at the Ajinomoto Stadium in Tokyo on November 3.

The All Blacks selectors have picked Barrett and McKenzie to cause England problems in terms of giving their team two options when it comes to running the backline.

If all goes to plan, this means there will be little chance of Barrett having to shoulder all the responsibilities in terms of making decisions. It also means that if England bury Barrett in a ruck, McKenzie can still move into the front line and slot into first receiver to call the shots.

By naming Richie Mo'unga on the bench, the All Blacks have another first-five capable of adding fresh legs and providing an insight into how to run the cutter in the second half.

"He's (Barrett) learning," Hansen stated. "It's the same for Richie too, they both want to play footy. And Damian is the same, they both love running the ball as opposed to using their kicking options. If you have only got one kicker, then it is easy to shut down those kicking options too.

GETTY IMAGES All Black Damian McKenzie charges forward during the Rugby Championship match against the Springboks in Wellington on September 15.

"From a team point of view it is just becoming a lot easier to do what we want to do, and therefore from an individual point of view it becomes a lot less frustrating."

With Barrett, McKenzie and Mo'unga all proven No 10s at international level, the selectors will be hoping they stay fit for the World Cup. The fact the All Blacks lost first-fives Colin Slade, Carter and Cruden with leg injuries during the 2011 World Cup hasn't been lost on Hansen, and he said the project of turning McKenzie into a test No 10 hasn't been shelved even though he is been named at fullback once again.

"Not really. The only thing that has changed is that a guy called Richie Mo'unga has come onto the scene. He is a world class five-eighth. Do we want Damian to continue to play first-five? Yep, because it gives him the ability to play what we want as a two-driving game.

"Those skills are still going to be much needed if he plays fullback."