Billy Vunipola insists he must overcome his cultural instincts as well as South Africa's giant forwards if he is to impose himself on today's QBE International at Twickenham.

By his own admission Vunipola underperformed in the 24-21 defeat by New Zealand which kicked off England's autumn campaign and was offered a combination of reassurance and harsh words by head coach Stuart Lancaster, who has demanded a reaction from his 22-year-old number eight.

Vunipola believes his inability to assert himself against the All Blacks is a result of his Polynesian heritage but is determined to throw off the shackles and carry the fight to the Springboks.

"I didn't enforce my normal game and felt I was quiet. It's tough because it's not in our culture to say 'look mum, I'm doing this'. As a kid you wait until you are spoken to," said Vunipola, whose dad and two uncles played for Tonga.

"Sometimes I have got too much respect for older guys in the team, but I have to say 'give me the ball, I'll do my best with it'.

"I need to impose myself with England like I do at Saracens and be who I am rather than tip-toeing round everyone.

"I have played the New Zealand game over two or three times in my head and there are times when I should have said to team-mates 'get out of the way, let me have a go'."

Vunipola is just 11 caps into his Test career, but the novice back row wants to be judged on his impact on a game rather than his age as he seeks to transfer the consistency he has shown for Saracens into the Test arena.

"I'm not still a kid even though people view me as a kid. People should forget I'm only 22," he said.

"It's fair enough that people are telling me I should be better because this is international rugby. I know I've got to be better. I know I could have been better against New Zealand.

"I'm more responsive to an arm around the shoulder than a kick up the backside. At Saracens I can sense they trust me.

"What made me feel instantly important at Saracens was before my first pre-season game they told me there was no pressure on me.

"They said they'd signed me because I'm an unbelievable player and because they trusted me.

"After that I didn't need them to tell me anything. I could sense by the way they are interacting that they fully trust me, although I'm not saying it's different with England."

England conduct their post-match reviews on Monday mornings by which point Vunipola will already have analysed his display in the company of his father Fe'ao, but only once his mother the Reverend Iesinga has conducted a service to her Methodist congregation in High Wycombe.

"I saw them last Sunday and it is something we have always done. I will always go to my mum's church on a Sunday and then after that we will be 100 per cent about rugby," Vunipola said.

"My dad is honest and if he thinks I was quiet, he will say I was quiet. If he thinks I played well, he will say I played all right. Hopefully I'll be better on Saturday and I'll have a different conversation with my dad.

"It's a lot to do with growing up fast. I feel like I have been around quite a long time."

One of the complaints levelled at Vunipola is over a perceived inability to last 80 minutes for England with Ben Morgan usually stepping off the bench as the final quarter approaches.

Vunipola insists he is fit enough to finish a game and if he is axed for Samoa and Australia, then he will seek a divine explanation.

"I want to prove myself. I told Stuart I want to be the Lawrence Dallaglio of the team, the guy who never comes off, the guy who plays 80 minutes and is the go-to guy," Vunipola said.

"I never fear being dropped because I think my faith is my priority. God for me is number one. Rugby is second.

"If I am dropped then maybe I am meant to be taught a lesson, maybe I am not being humble, maybe I am getting ahead of myself hence I played badly."nds