It has fast become rugby's great puzzle - how do you stop Andy Farrell's Ireland? The green giants of the Six Nations march towards history and a second consecutive grand slam with inexorable intent, carrying the confidence and certainty befitting one of the best teams of the modern era.

In the last two years, their record reads played 25, won 23, lost two; the last time Ireland lost to someone other than New Zealand or France, Joe Biden had been in office for a fortnight. How do you beat them? The answer at the World Cup was to produce something resembling rugby perfection. In the All Blacks' quarter-final win in Paris, New Zealand turned the ball over thrice in 80 minutes; they did not allow Ireland a single scrum feed. Ireland were rattled, ruffled and roughed up, but were the girth of Jordie Barrett's thigh away from victory; New Zealand still required a remarkable 37-phase defensive stand to cling on at the end. Good luck England. "Let's be clear," Steve Borthwick said in open-eyed acknowledgement of the challenge ahead of Ireland's arrival at Twickenham on Saturday. "Ireland right now, we can all agree, are the best team in the world. They might not have won the World Cup, but the way they've been playing through the first period of this championship, they are the best team in the world."