Yokohama - England coach Eddie Jones may have christened his flankers Sam Underhill and Tom Curry the "kamikaze kids", but number eight Billy Vunipola gave them a new nickname after Saturday's semi-final win against New Zealand - the "Duracell bunnies".

Curry and Underhill were again everywhere in England's stunning 19-7 victory over the defending champions, happily for Vunipola who joked that their intense work-rate allowed him to have a breather.

"It's made my job easier so I'm happy that I'm on their side, those guys. They are like the Duracell bunnies, they just go all day and that allows me to rest and hopefully I can make use of that by helping in other ways," said a tongue-in-cheek Vunipola.

"I just kick back and watch them do their thing," said the rampaging number eight, who won his 50th cap on Saturday.

The 26-year-old Saracens forward is the grand old man of the dynamic back row - Curry is 21 and Underhill 23 - but he said many in the England set-up looked up to them despite their age.

At an average age of 22 years and 107 days, Curry and Underhill are the youngest flankers to start together in a Rugby World Cup knockout match.

"The work they put in is quite inspiring. Not just for me but for everyone else in the team," said Vunipola.

"I hope they have many more caps ahead of them and they stay injury-free because at the moment, they are smashing it," said Vunipola.

He joked that they had both started out in the gym at an early age - ribbing Underhill for "having no neck because his back's so big".

Vunipola added that he was honoured to win his 50th cap, especially as he has been plagued with injury recently.

Asked if his family would be out to join them, he passed the question to brother Mako, an England prop.

"I don't deal with it. My brother deals with it. That's why it's nice having him here because all the admin goes through him."

"I just focus on getting haircuts and things like that," said Vunipola, whose hair is distinctly shaved at the sides and long at the back.

The relaxed Vunipola said that being so far away from England made it easier to handle the pressure, as they were far removed from the hype back home.

Asked how he spent the week, he said he was "spending a lot of time in the team room, had a lot of coffees. Had a few chocolate bars and that this week.

"That's how we stay out of the limelight."