It's next stop Las Vegas for the cuppa crusaders

The look on the security guard's face is impenetrable as he peers at our custom-made tea wagon through pitch-black aviator glasses.

He hasn't heard of Yorkshire Tea, it seems. He must have heard of Yorkshire, though, surely?

"No sir I have not," he says gruffly, hand on holstered revolver, gingery moustache bristling in the desert breeze. "So you got a permit for this thing?"

Fortunately we have bought our vehicle permit well in advance, and after making some vague and ultimately empty threats to search our bags anyway – presumably hoping to find an ounce or two of illicit high-grade Earl Grey – the checkpoint guards grudgingly wave us through and we are back on the road with 'Little Urn', the converted ice cream van heading across America.

This particular checkpoint stands at the entrance to the Hoover Dam, an astonishing 726-feet testament to American ingenuity.

The sight of the tiny red Yorkshire Tea wagon below making its way slowly across the dam from one side of the impossibly deep-sided canyon to the other merely adds to the grandiose effect.

Indeed, the scale of this whole sprawling country is brought crashing home as we realise that by crossing the state boundary between Arizona and Nevada as we drive from one side of the dam to the other, we now find ourselves in a different time zone.

Arriving at the public car park on the other side of the dam – an hour earlier than when we left – the American tourists are fascinated and confused in equal measures by the sight of Little Urn.

"Wow, you guys must be British, right?" one lady says, utterly delighted to see us living up to our national stereotype so completely. "Can I get an ice cream?" asks another.

Little Urn is far from the only odd-looking form of transportation in the car park, however . A policeman is on patrol on a Segway, the upright, two-wheeled "personal transporters" which are becoming increasingly common sights in parts of the US.

"I love it, man!" he beams, looking ridiculous as he scoots happily around. "It's better than sitting in a squad car all day, that's for sure.

"This baby took me 30 minutes to learn to drive, and it has never let me down."

Indeed, the officer seems to have found a deeper, philosophical connection with his scooter. "You just have to trust it," he tells us, wheeling back round and pulling up smartly.

"You have to lean forward like you feel you're going to fall, but then you just have to go with it. That's the key. Once you learn to accept death, it all falls into place."

He nods wisely. We take his word for it, and press on into the desert.

We have driven some six hours or so since leaving Los Angeles, watching as the green Hollywood hills slowly gave way to this dusty, barren scrubland.

The arid feel seems to permeate everything, and the driving quickly becomes thirsty work.

Time for a brew then, surely?

Sadly, not – it seems Little Urn's tea-making equipment has suffered a temporary malfunction, and we will have to go without until we reach the next city.

Feeling slightly treacherous, we console ourselves with takeaway coffee from a local service station, safe in the knowledge that the bright, bright lights of Las Vegas are now just a few miles away.