Firstly, our presence on Cannes' famous Croisette has nothing whatsoever to do with any films. Secondly, I hadn't actually heard of the car I was heading to the French Riviera to drive - the implausible-sounding Dartz Prombron Iron Diamond. Thirdly, said vehicle comes with some interesting optional extras.

In no particular order: a kilo of top-quality caviar, a $1.3m bottle of vodka and last, but most definitely not least, a custom-made dildo. Marketing types like to refer to a car's clever little extras as ‘surprise and delight' features. This gives new meaning to the concept.

"Russia has a very different mentality," he says, his Eastern European accent effortlessly cutting across some Europop. "If you want to do a new beer, a new water, a new Coke... you can do anything. It's the same with the car. The Kombat gives this possibility to Russian guys. We will make it more luxurious, but still with a strong security element."

The Iron Diamond, of course, also has a strong sex-toy element, but this is just a showcase for, er, what lengths Dartz will go to for a customer. On this version of the car, you pay $1.3m for the vodka and marital aid and get the Kombat thrown in. A clever headline-generating ploy; lesser Prombrons start at $700,000, and take between three and six months to build.

And though this is the supposedly ‘luxury' Prombron, no one is going to mistake it for a Range Rover. Yes, there's leather on the seats, bits of wood trim, and a gigantic TV and audio system can be specified. The ride is inexplicably good, the sheer mass of the thing simply obliterating bumps, and it even sort of handles.

But it feels like a giant bank vault on wheels, it has girders where its windscreen pillars should be, and feels so thuggishly well screwed together that a bomb could go off under it and you wouldn't notice.

Which brings me onto the security question. Depending on what level of armour you've specified, a bomb actually could go off underneath it. You would definitely notice, but at least you'd survive to take out a hit on whoever was responsible. (That was a joke. Honest.)

The security industry grades armour plating B1 to B7; B1-3 gives you thin armour plating, four doors, and opening windows all round. B4 onwards upgrades the thickness of the armour, restricts the bodyshell to three doors, and permits only the driver's window to open. Our ‘test' car is B5-plus, so you need two hands to pull the doors shut, sitting in the back ironically increases your anxiety because it's so claustrophobic, and the driver's window is a thumping five centimetres thick.

"About 70 per cent of the people want the armoured material just because they can," Igor says, "and maybe 20 or 30 per cent of them really need it. The market we're really interested in is Brazil. Everything in Brazil is bulletproof. Even the Smart cars."

While rumbling up and down Cannes' famous Croisette promenade, it suddenly occurs to me that we could wreak untold havoc on this place and probably get away with it. Anarchic thoughts of parking our Russian tank on the festival's red carpet give way to simple, pathetic posing; although this is primarily a forum for film producers to buy and sell their wares, it's also where Europe's rich - idle or otherwise - have come to see and be seen.

In the marina, we discover that there are some forms of transport that even a giant Russian SUV can't compete with, and on the far end of the jetty, a super-yacht waits to decant its owners into a waiting Rolls Phantom and Ghost, and not one but two McLaren SLR roadsters.

Back on the promenade, the premiere of the festival's eventual Palme d'Or winner, Terrence Malick's grandiose The Tree of Life, draws the stars out for the waiting horde. As it happens, we're dropping some old friends, film-maker Mark McQueen and producer James Mann, to a party. The Prombron is not ideal limo material, but an amusing foil to the fleets of dreary official Renaults.

At one point, I find myself cheek by jowl with the world's most powerful media baron, Rupert Murdoch. A potential Prombron man, if ever there was one. Ten minutes later, photographer Lee Brimble and I wade through the masses who have been waiting all afternoon to catch a glimpse of Brad Pitt and Angelina Jolie. We're there no longer than five minutes, and Lee gets his shot.

And that's TG's Cannes in an armour-plated nutshell. The stars, a ridiculous but curiously enjoyable car, in 12 hours. There's only time now to tank it back to the airport. And for the first time ever, we actually have a tank in which to do it.