All Blacks assistant coach Steve Hansen called for two referees to be tried in test rugby, believing the speed that the game is now played at has got too quick for one whistleman to handle it.

Hansen made his bold suggestion in the wake of the All Blacks' 22-3 win over Ireland in Dublin.

That gave New Zealand the second leg of their Grand Slam dream and as the team moved on to Limerick to play Heineken Cup champions Munster on Wednesday (NZ time) the All Blacks, who clearly play the quickest game in the business, were happy to offer thoughts on how things could be improved at the highest level.

While the scrums were the subject of post-match talk following their opening win in Scotland, the breakdowns were a touchy subject from the win over the Irish where Hansen described them as "a bit of a mess".

The All Blacks also appeared bemused at a try not being awarded to Ali Williams.

When asked how things could be improved, Hansen went revolutionary with his solutions.

"I think two referees would be good. I'm not blaming the ref (South African Mark Lawrence) for yesterday," said Hansen.

"But the game has changed in so many ways. It's got much faster there are so many new laws. Yet the one thing that we haven't changed is the referee. He's still doing what he has always done.

"I think it might be time to look at saying well, we might need two officials on the park."

Hansen noted that other sports had gone down this line and Australia's NRL rugby league championship is looking at a proposal to have two referees on the paddock.

The All Blacks have had informal discussions with IRB refereeing boss Paddy O'Brien on this tour. Hansen said O'Brien had acknowledged that things need to change.

"It's getting difficult, it's just the speed of the game," said Hansen.

"It's bigger, faster, stronger. You only have to watch footage of three years ago (to appreciate that).

"I think we need to start looking at ways of helping our referees do what is a difficult job."

Hansen then went a step further by suggesting that neutral referees weren't required as long as the best were used.

"I would personally like to see the IRB take the top 10 referees in the world and put them under Paddy and say, 'right you are doing all the tests'.

"The top six do all the top nations and if you don't go any good, you drop back down to seven, eight, nine and 10 and you get yourself better."

Hansen said it was a flawed system where players could quickly attain 50 tests while the top referee took a lifetime to approach that number and most didn't get near that level of experience.

"I find that somewhat bizarre."

The All Blacks win over Ireland wasn't without its moments in officiating in a test played at a furious pace and with huge physicality, particularly in the tackle situations.

Both sides had players sin-binned, a penalty try was (correctly) awarded to New Zealand but tries were also denied and once again some of the breakdowns appeared to be a bit of a lottery. There was the now standard pre-match barbs at Richie McCaw. This time they came from former Wallabies coach Bob Dwyer who believes the All Blacks skipper is persistently getting away with cheating in his work over the ball.

But that was all academic to the All Blacks who have taken another step in their goal to become just the third New Zealand side to achieve a Grand Slam.

Wales are next up this weekend with England to follow. With the All Blacks' form building nicely, it's hard to see either of those sides stopping them.

Hansen described the three-tries-to-none victory at the massive Croke Park as "a handy enough performance".

"We could have in fact we did score two more tries but they weren't ruled that way. That was a bit disappointing. But there were other opportunities as well and I don't think we were quite clinical enough.

"We try to do everything picture-perfect and when you do that sometimes you don't quite finish it off."

Hansen felt the game had spluttered along at times. The All Blacks struck either side of halftime to take control after dominating most of the first half without much reward. The game finished with a flat final quarter.

While the All Blacks were reasonably content with their own work, Hansen couldn't resist a parting shot at the Irish, despite talking them up for most of the buildup to the test.

"I know this sounds a bit disrespectful but they were just trying to survive," he said. "I talking to them last night they were reasonably shocked at how physical we were and in the end they just tried to get through that."