"I'm afraid Mr Schwarzenegger got stuck," an aide tells me, and I immediately find myself wondering: in what?
Images spring to mind of the 6ft 2in 18-stone Hollywood icon and former governor of California striding through this dainty Knightsbridge hotel and getting lodged in a door frame, or having to be cut free from a minicab outside with a circular saw.
But, in fact, he has just been detained by a prior engagement: a video shoot for the LADbible website in which he was filmed eating traditional Austrian and American snacks and desserts, before choosing his favourites.
"They totally screwed up my diet!" he chuckles, ploughing into the room. "Kipferl cookies, Oreos, Twinkies, Sachertorte."
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Schwarzenegger is 72, and has been "99 per cent vegan" for the last three years, though he still looks as if he subsists on a diet of molten steel and breeze blocks. A household name since the mid-Eighties, he has a life story that remains astonishing today: the boy born into postwar Austrian poverty who slogged, flexed and wisecracked his way to the summits of American celebrity and public life.
Perhaps thanks in part to those eight years as the Governator, his presence is very different from the usual movie star showbusiness aura. Everything about him suggests things are about to get done, and properly: you can feel the very atmosphere in the room sitting up and straightening its tie when he arrives.
He has come to London on the global press tour for the latest Terminator film, subtitled Dark Fate, which sees him return as the deadly T-800 cyborg assassin, the role that made him a star. Dark Fate finds him living in a log cabin in the Texas wilderness, with Old Glory billowing over the porch, then summons him back for one last rodeo - with 63-year-old Linda Hamilton, no less, who returns for the first time since 1991 as Sarah Connor, the T-800's former ally - and, before that, target.
Despite Terminator 2's extraordinary box office success, Hamilton's career ebbed in its wake: much of her next decade was taken up with television work and a relationship with James Cameron, the director of the first two Terminator films and co-creator of the character, which culminated in a brief marriage.
Hamilton was absent for the franchise's recent unfortunate flounderings. But her role in Dark Fate, its sixth instalment, signals its welcome return to first principles. Like the first two, it is a science-fiction chase thriller, in which a revolutionary uprising may or may not be pre-emptively quashed by a homicidal robot skeleton from the future.
For Schwarzenegger, the enduring appeal of the original Terminator films is something also central to Dark Fate: the paradoxical nature of time travel itself.
"You have to really think how it all fits together," he explains. "Like in the new film, when Linda says, 'The future never happened' - that means there was a future from which they sent the Terminators back to the present, but because of what happened in the present it actually never existed. Heavy s---, right?"
It was Cameron, a producer on Dark Fate, who convinced Schwarzenegger to return. Because Terminators age like humans - the T-800's terrifying chrome frame is covered with living tissue - no digital de-ageing was required. Quite the opposite, in fact.
"I went to the set with my hair coloured and they started painting the grey back in," he laments.
A new Terminator film might not be the first place you'd think to look for topical commentary, but one of Dark Fate's boldest and most surprising sequences takes place on the US-Mexico border. It involves the heroes breaking out of a detainment centre: cages are flung open, patrol officers thwarted, imprisoned migrants freed.
For Schwarzenegger, this is a classic Cameron touch.
"Jim writes deep," he says, likening it to his decision to cast Hamilton as an action heroine in 1991, "when no one else in Hollywood would have dared take that risk. He writes the world as he sees it."
Does he think the scene might prove commercially risky in the United States, where border security has become a major point of contention?
"It's reality," he shrugs. "Some films hide those kind of realities, but Jim says, 'Let's put it out there.' He doesn't f--- around."
Nor, when it comes to politics, does Schwarzenegger. The actor sounds practised at trotting out his record as governor - environmental and energy reforms, improved infrastructure, the push towards bipartisan cooperation - and recently described himself as "kinda the first populist that was elected". But I'm not sure he's right about that.
His collaborative style in office is wholly at odds with the vituperative "pick a side" politics of the moment. "Post-partisanship" is even one of the pet causes of his new academic think tank, the Schwarzenegger Institute for State and Global Policy. The US Constitution holds that only natural-born citizens can become president, so failing an amendment - of which there was once some talk - his time on the political front line is likely over.
He still considers himself a Republican, but says the party under Trump "has veered off in another direction".
"Trump is in there creating an extra trillion dollar deficit and the Democrats are the ones screaming, 'Wait a minute, you're spending too much money.' "
He hopes for a realignment "when the craziness is over", though he remains to be convinced that will come about as a result of impeachment.
"It all depends on what they find out - what the realities are as opposed to the hype on television," he says. "I just hope for America's sake that we get through this as quickly as possible and find a way to bring the two sides back together. Because right now we are at a dangerous standstill."
Teamwork and compromise are things he'd learnt to value three times over by the time he became famous, he says: on the bodybuilding circuit, where "Everyone had the chance to win Mr Universe or Mr Olympia"; in business, "where you sit down and work things out rather than looking at the other side as the enemy"; and in his 25-year marriage to Maria Shriver, a lifelong Democrat and niece of assassinated US President John F Kennedy.
(Shriver filed for divorce in 2011 when it came to light that Schwarzenegger had fathered a child with their housekeeper in the Nineties: nevertheless the split has yet to be finalised, and they remain technically still married.)
As for fantasies of strongman deliverance and rule - well, that's what his films are for, Schwarzenegger suggests. At a test screening of the first Terminator film, he says, an audience of around 80 Los Angeles cops cheered on the T-800 as he destroyed one of their police stations.
"They loved the idea," he recalls."But everyone is frustrated with their job, or angry with their neighbour, and wonders what it would be like to just, you know, take care of business. Everyone has those little dreams."