With eyes closed and lips pursed, Vin Diesel, the might behind the Fast & Furious muscle cars, seems to be in a world of his own as he whistles a cheerful little tune.
The native New Yorker opens his eyes and grins. "I hope this will be an interesting interview. Anything less will be unacceptable," he says in a British accent that swings from upper crust to East End "mockney".
It's a surprising introduction to one of the globe's biggest action stars - but the hulking form of Diesel has a lot to be cheerful about.
Twelve years ago a small film called The Fast and the Furious about underground street racing in Los Angeles, and starring Diesel as racer Dom Toretto, became a sleeper hit.
The franchise has picked up so much speed the just-released No. 6 has raced passed the $US500 million ($530 million) mark faster than any Universal movie in history. It's an achievement worthy of praise.
"Why, thank you," says Diesel, "Isn't that crazy beautiful. Isn't that surreal," he says shaking his bald head in disbelief.
"I mean how did that happen? I think we're proving we can have cutting-edge action without sacrificing story arc. That's one of the things we're all proud of in this saga," he says in his deep American growl.
In the last instalment, Toretto, along with his best friend, the former cop-turned-racer, Brian (Paul Walker), and their crew toppled a Brazilian drug lord's empire. While the heist left them with $US100 million, they were banned from stepping foot on US soil.
Meanwhile, Toretto's nemesis, Federal agent Hobbs (Dwayne Johnson), has been tracking an organisation of lethally skilled mercenary drivers. Masterminded by Owen Shaw (played by Welsh boy Luke Evans), it's soon revealed his second-in-command is none other than Letty (Michelle Rodriguez), Toretto's lost love who he thought had died in 2009's Fast & Furious.
As a producer, as well as star since that fourth instalment, Diesel, 45, was keen to revisit the Dom-Letty storyline.
"Theirs is a cherished love. The fact it exists on the wrong side of the tracks makes it more intriguing," says Diesel, who has daughter Hania, 5, with Mexican model Paloma Jimenez.
And so Dom and Letty meet again - this time on opposing sides and on the gritty streets of London where Hobbs has asked Toretto to assemble his elite team to overthrow Shaw.
While the franchise has evolved from a street-racing film into a global action thrill ride, it was paramount to Diesel that they never lost sight of their core characters.
"We're all wanting to go one up on what we did in the past and, at the same time, continue and evolve the characters and the story in an interesting way and in a way that's true to the franchise," he says.
"It's gratifying to be able to look back and to see how everything links up."
A sixth instalment of any blockbuster franchise is an enviable position to be in but not one to take for granted. It says something of his (and the franchise's) status that Piccadilly Circus was closed in order to shoot a racing scene through the capital.
Diesel's grounded attitude could be due to the fact he didn't have a smooth ascent to superstardom. Diesel - or Mark Sinclair Vincent as he was born - began acting when he was seven "but went 20 years without getting a job". In the interim he worked as a bouncer, dropped out of an English degree and failed to kick-start his career in Hollywood.
On his return to New York, his mother gave him a book on launching a film career by making your own movie. He went on to write and direct a short film, Multi-Facial, based on his experiences as an actor, (he'd often been told he was "too black" or "too white" for parts).
Steven Spielberg saw it at the Cannes Film Festival in 1995 and created the role of Adrian Caparzo, with Diesel, in his World War II movie, Saving Private Ryan.
"That was, as everyone knows, my first paying acting job," Diesel says. He was then cast as the voice of the title character in The Iron Giant role before winning the lead of Riddick in 2000's Pitch Black.
It's a role he reprises for the third time this year, as well as returning to the role of Xander Cage in the sequel to 2002's xXx.