Jumbos and trunk roads

"Are you sure that's unleaded?"

We compared the hieroglyphics on the hand-operated petrol pump to the stern warning on the petrol tank. On the mainland, pumps were labelled in English - but not on this island. "You see that letter that looks like an elephant - there's no elephant letters on the pump."

Thus we narrowly avoided pumping agricultural diesel into a new Kia Jeep.

I figured that renting a car was the best way to get to know Thailand; the freedom of a backpacker without lugging your own bags, the luxury of a tour where you plan your own itinerary. I remembered the smile fading from the face of Nuchkamol the Avis rep as my sister Dallia called from the window: "What side of the road do you drive on, again?"

And the sudden rush of freedom was intense. I was so excited I didn't check for a map. In what the Thais laughably call the cool season, we left behind the seedy seaside resort of Pattaya in a cloud of dust, the hazy glow of sunset rose-tinting our rear-view mirror. Swerving oncoming Song-Taew taxis suggested that I might stick to the left-hand side of the road.

Fearing the worst of the Phuket/Samui trail we decided to head east, following the coast towards the Cambodian border instead. But in Thailand you get easily distracted. A growing addiction to Thai food meant that every roadside stall became as vital a cultural experience as the gargantuan golden temples that appear out of nowhere. Our progress was wonderfully slow. A tour guide would have been chewing his clipboard in frustration.

In a loose adaptation of an ancient Irish driving game, any signpost or billboard bearing the image of an elephant was met with the cry "chang", the only Thai word in our vocabulary. After 30 kilometres I was the reigning world champion with 17 confirmed changs.

But what we really needed was a map. From seaweed-flavour crisps to jasmine slurpees, there's little you can't get in the massive airconditioned petrol stations that line the main roads. And, like everything in this country, the prices are plain silly. What fuel crisis? A full tank of petrol costs a fiver and Dallia's daily nicotine fix about a tenth of that. But, for love nor money, I couldn't find a map.

Bizarrely, however, one petrol station did have a state-of-the-art photocopier, so the attendant copied her own road map for us. Thai people are remarkably friendly and the further you get from the Bangkoks and Pattayas of this world the friendlier they get. Children squashed into the backs of pickup trucks waved and giggled as we passed."Chang!" yelled my sister. She tugged my arm: "No, really, chang!"

We stopped the car as a baby elephant came and nuzzled against the jeep while she fed it

Night driving presented different problems. With no streetlights out of town and limited road markings, it was hard to tell where the dusty road ended and wilderness began. This was not helped by the beguiling Thai tradition of flashing your lights madly at any driver you meet. Just to say hello, apparently. Mainly we held on and hoped for the best. They really could kill you with kindness.

We rolled into Chanthaburi in time for midnight mass in the neon-lit cathedral. Chanthaburi is a Catholic town in a Buddhist country and they've managed to make even Catholicism all touchy-feely. Little Frank and his sister Geve, dressed in soldier suit and angel-wings respectively, showered us with Halls Mentholyptus sweets. At the bustling night market - just as good as the best restaurants except for the cutlery - we consumed our own bodyweight in green curry before we hit the road again.

Thailand isn't the primitive place you might expect. Modern cars ride well-paved roads and main routes are well signposted, despite a mischievous tendency to place the signs just after your turning. Our copied map, however, turned out to be more an entertaining work of fiction than of any practical use, but one thing caught our eye: Koh Chang - an island called elephant.

As the sun rose through the mangrove forests, mist lifting from the road, we arrived at the car-ferry port of Laem Ngop. The mention of which never failed to reduce Dallia to shoulder-heaving convulsions. After 20 minutes at sea, the lush green triangular profile of Koh Chang rose in front of us.

We drove mountain roads, over bridges, beneath forest waterfalls and through rocky river beds until the beaches began. By which time I felt like a cross between MacGyver and Eddie Irvine.

Then the inevitable occurred. As the bridge ended so did the road, leaving us half way down a river bank at a 60 degree angle. As I sat contemplating eternity and watching my loving sibling desert the sinking ship, a pickup truck appeared and pulled me back from the brink. As I embraced my saviours, I wondered how they got there so quickly.

"Well," explained Dallia, "They'd only just finished digging the thing."

We'd fallen into the original Thai tourist trap.

Avis Rent A Car (0870 60 60 100) has more than 30 outlets throughout Thailand. Prices from £200 a week for an air-conditioned car, including unlimited mileage, collision damage waiver and tax. EU driving licence required.