They are people you see at work for two and a half seconds. If they take three seconds, they are in trouble. If they take four, their jobs are at serious risk.

A Formula One car will speed into the pit lane between three and four times on every grand prix, where crouching and waiting, are a helmeted team who will remove all four tyres in the passing of a breath.

Paul James will be in charge of the McLaren pit crew for Sunday’s United States Grand Prix in Austin, the crew’s “guardian angel” as he describes himself. He is a humorous, softly-spoken Welshman from Llanelli but James could not have kept his place in the McLaren pit lane for 18 years without some steel. He will forgive a mistake, he says, but adds: “there won’t be a second.”

When Jenson Button lost his wheel at Silverstone, that was my fault... That was me. <p>Paul James</p>

Talking at the team headquarters, a futuristic sweep of glass and white tiles in the Surrey countryside, James smiles when he admits to his own worst error, during the 2011 British Grand Prix. “When Jenson Button lost his wheel at Silverstone, that was my fault. I lost a wingnut when I gunned his wheel and the front wheel came off when he left the pit lane. That was me.”

Such is the extraordinary pressures to change four tyres three times in every race that it seems astonishing there are so few errors. During this month’s Japanese Grand Prix, there was a breakdown in communications between Button and the pit crew. They usually have 14 seconds to take a tyre to the pit lane. At Suzuka they had 12. They made it - just. The pit crew undergo much the same level of fitness training as the drivers and are contractually obliged to train three times a week at the Technogym suite at McLaren’s headquarters.

The biggest change in James’s time at McLaren has been the ban on refuelling. “With refuelling you were quite comfortable,” he said. “You could take up to four seconds. Now we aim for two-and-a-half seconds but Williams and Mercedes are two seconds now. They have different equipment – quick release jacks, where you press a button to release them. That’s something we are going to invest in.”

James has spent the last 18 years in McLaren's pit lane (Getty)

The last few seasons have, James conceded, been ‘brutal’ both for pit crews across the sport and for McLaren in particular. They last won a grand prix in November 2012. The Brazilian Grand Prix was taken by Jenson Button, who unlike virtually all the rest of the grid did not come in to change his tyres when light rain began falling over Interlagos. Added to that was the failure of Sebastian Vettel’s radio which meant the Red Bull crew were not ready when he turned into the pits.

“There have been races when you do make the difference,” James said. “In the Malaysian Grand Prix earlier this month, Force India entered the pit lane just ahead of us but we left before them. We finished seventh and they finished eighth.”

Grands prix have expanded in number and across the globe. Once there were 14, the majority in Europe. Now there are 21 and the demand will continue to be for more. “Jet lag is a killer,” said James. “Logistically, 21 races is a nightmare. With 21 races family life is tough. The car will be flown out on a Monday and the crew will fly out on Wednesday. The chassis is shipped out and the engine is fitted trackside.”

All work has to be finished before the 11pm curfew but since McLaren’s switch from Mercedes to Honda engines, Paul James’s team have often run very close to the deadline. “Previously we never used to touch curfew. Now we are running up to it every night finishing 10 minutes before. We work every hour constantly. It is a lot calmer now because we are making progress but it was hard last year.”

McLaren have not won a grand prix since Button's victory at Interlagos in 2012

Pre-season testing, usually carried out at the Circuit de Catalunya near Barcelona or in Bahrain, is especially draining. “It is the worst time for a mechanic because it runs all day and you rebuild (the engine) all night so we run a shift system,” he said. “Twelve hours on, 12 hours off. The car is worked on 24 hours a day, four days a week.

“I have seen more movement in personnel in the last three or four years than at any time in my career. People are leaving the sport altogether. Before, we would keep a team together for 10 years but now with 21 races and three to four tests on each, the attrition is quite high now. People are going back to lower formulas or factory-based jobs. Red Bull and Mercedes are suffering from the same problems.

“When you recruit replacements, you look for someone who is, above all, calm and focused. You can tell when you first meet someone whether they are going to adapt to the pressures of the pit and, equally, you can almost tell by the way someone walks up to you that they are not going to make it.

“When they are changing a tyre some of the guys even stop breathing for those two to three seconds and there is a limit to how much quicker you can go given the limits of human hand-to-eye co-ordination. I think two seconds is as far as you can push it.

"Red Bull have done 1.95, Williams have done 1.92 but they have done it once. The gunning time should be no longer than 0.2 of a second and human reaction, at its quickest, is between 0.2 and 0.3. You are asking a lot.”