Jofra Archer will become a World Cup finalist less than three months after making his international debut, but England's leading wicket-taker at the tournament does not expect nerves to be a problem.

Archer only joined his new team-mates for the first time in May, after changes to the governing body's residency rules fast-tracked the Barbados-born seamer's eligibility, but has made a stunning impact.

The 24-year-old has already set a new England record with 19 wickets at the tournament and excelled on his biggest stage to date, dismissing Australia captain Aaron Finch lbw with his first ball of Thursday's semi-final at Edgbaston, before returning to see off the dangerous Glenn Maxwell.

A crushing eight-wicket victory set up a winner-takes-all date with New Zealand on Sunday and it will be no surprise if Archer is the coolest man at Lord's.

"I don't think it's really sunk in yet. But the calmer you are the better you are in these situations," said Archer.

"I just think I've always been like this. I try not to get nervous because then you end up doing stuff that you are not really supposed to do.

"Butterflies? Not really. Even when we were at breakfast before Australia...I may be wrong but I don't think anyone looked nervous. Everyone just looked focused by the time we got into the ground. It's those little things that make you feel like the guys are really ready."

Archer's on-field demeanour typically matches his measured words off it, but even he admits that sending the Australia skipper back for a golden duck set the adrenaline racing.

"Emotions were definitely flying after that," he said with a smile.

"It definitely pushed the team. Everyone was just a lot more focused and switched on. I'm just glad the team is going well.

"I could be doing terribly as long as the team is winning. That would be alright. I'm just happy to play games and win games."

It seems increasingly likely that Archer will get another crack at Australia during the forthcoming Ashes series, with the only real question surrounding his fitness, not his ability.

There is a growing clamour to unleash him in the Test arena but he has been managing a side issue throughout the last few weeks and England may choose to delay his introduction.

"After Sunday, I'll probably answer that but for now I'm just focusing on trying to win the final," he said.

"I'll keep soldiering on. I have been for a few games now and it's not got any worse. I was probably going to rest any way but I don't think Sussex are going to flog me right now.

"I think I may get a well-deserved rest."

Very little has surprised Archer since he landed on the global stage, but he did express bemusement at the interest in mining his past social media posts.

His prolific use of Twitter as a cricket-mad youngster has given rise to the notion that there is 'an Archer tweet for every occasion', often referencing his current team-mates and opponents.

"I have seen this but I don't know why this should be a big thing! It's just social media, that's all it's there for," he said.

"I used to do it when I was just watching cricket back home. I wasn't even in England for half of that stuff."

Asked if there would be a fitting message to mark England's first World Cup win in a couple of days' time, he grinned and added: "Definitely".

Jason Roy will be reunited with umpire Kumar Dharmasena in Sunday's final, after the Sri Lankan was appointed for the Lord's showpiece.

The pair were involved in a tense moment during England's semi-final thrashing of Australia after Dharmasena incorrectly gave Roy caught behind on 85.

Both batsman and official appeared to be unaware that Jonny Bairstow had already used England's DRS review, with Roy making the signal and Dharmasena sending the decision upstairs – a process that was only quashed after a reminder from Australia's fielders.

Denied the chance to make the highest-profile century of his career, Roy remonstrated long and loud before trudging off the field in a state of barely concealed fury, with stump microphones picking up an apparent obscenity.

The 28-year-old was fined 30 per cent of his match fee and handed two demerit points on his disciplinary record as a result, sanctions he accepted at a post-match hearing.

Dharmasena will stand alongside South African Marais Erasmus. Rod Tucker will be the only Australian to see action in the finale, taking up the third umpire's chair, with Pakistan's Aleem Dar (fourth official) and Sri Lankan Ranjan Madugalle (match referee) also chosen.