‘Reason I canceled my trip to London,’ Donald Trump tweeted last month, ‘is that I am not a big fan of the Obama Administration having sold perhaps the best located and finest embassy in London for “peanuts,” only to build a new one in an off location for 1.2 billion dollars. Bad deal. Wanted me to cut ribbon-NO!’ The only fact he didn’t get wrong was the cost of the new US Embassy in Nine Elms. It looks like a billion dollars, too. From Vauxhall, the shiny green cube brings to mind an enormous pallet of dollars from a movie, but with a seemly swathe of translucent plastic skin on three sides. Up close, though, the skin stretches away from the glass uncomfortably, and the effect is more reminiscent of the piratical accountants’ building at the beginning of Monty Python's The Meaning of Life.

You get invited to the embassy if you want to go to the United States and don’t qualify for a visa waiver, for example if you have a British passport but have travelled recently to a country on America’s naughty list: Libya, Iraq, Somalia, Sudan, Syria, Yemen or, as I did last year, Iran.

Rounding the moat on a wet Wednesday morning, I joined the rest of the huddled masses yearning to go through the security scanners and get inside. It’s hard to resist the thought that they like to see you queuing up: they wouldn’t want it to go full Saigon, but just a little reminder that it’s better inside than out. After forty minutes in the drizzle I turned to the young man next to me: ‘What did you do wrong to end up here?’

“What? Nothing,’ he said. ‘I’m working at Camp America in the summer.’

Once divested of water bottles and other suspicious objects, you can proceed through to the citadel. Clean, monolithic, sympathetically lit; the feeling of solidity is undermined only by the rubber padding covering the inside of the glass lifts, as if they’re worried about accidents.

The former US embassy in Tehran has a different vibe. Instead of inspirational quotes from RFK, there are anti-American and anti-British graffiti. The new curators have restored it to the way they imagine it looked when the American mission was still there, with mannequins dressed as Iranians attached to electrodes, and mannequins dressed as CIA agents at the dials.

‘Where are you from?’ a man asked me.

‘Um, France,’ I replied, Frenchlessly.

They'd be hard pressed to redecorate the Nine Elms building like a torture chamber, at least the bit I was in. The visa hall is an almost celestial white and I didn't see a single plug socket. I’d already filled in my DS-160 form online, with its variously searching questions:

Do you belong to a clan or tribe?

Have you ever been directly involved in the establishment of population controls forcing a woman to undergo an abortion against her free choice or a man or woman to undergo sterilization against his or her free will?

Some of them sound like a late Pinter poem:

Have you ever ordered, incited, committed, assisted, or otherwise participated in genocide?

Have you ever committed, ordered, incited, assisted, or otherwise participated in torture?

Have you committed, ordered, incited, assisted, or otherwise participated in extrajudicial killings, political killings, or other acts of violence?

They have other questions that you can’t just answer ‘no’ to, which they save for a face-to-face interview. ‘Why were you in Iran?’ the man at the desk asked me.

‘Tourism,’ I said. I told him that would also be the reason for my travelling to the US. No, I probably wouldn’t be visiting my aunt in Indiana.

‘OK. How much money do you earn?’

I told him I did voiceover work and we talked about Redd Pepper, the voice of a thousand movie trailers. For some reason I imagined he’d died recently, and said so (it turns out that he’s very much alive; I hope that doesn’t count as supplying false information). The embassy official and I commiserated with each other, and he said that my visa had been approved.