When I travel, I’m so bloody English it’s embarrassing. It’s very hard to blend in with the locals in Kenya or Mexico when you’re 6ft 7in tall and a pasty, off-white colour. I burn easily so I avoid the sun, which means I never have a tan. I get heat rash. Bugs bite me. I always get sick. On my last two trips abroad I got foot infections so now I wear shoes and socks with my shorts. I don’t drink the water. I worry a lot about what the toilets will be like. I wear a money belt hidden under my shirt. There are some wet wipes in it. I pack a supply of PG Tips in case I can’t get a decent cup of tea. I am a cliché. I prefer two weeks in Devon. So why am I on an 11-hour flight to Vietnam? I have no idea but I am nervous. Wasn’t there a war there recently?

This is my first trip to south east Asia. I’m with my girlfriend, Claire, and we fly into Hanoi. As we leave the airport, the heat wallops me in the face like a giant hot towel. (There are lots of actual hot towels in Vietnam. People hand you hot towels constantly. In hotels, restaurants, everywhere. You will never want for hot towels.) The Hanoi sky is overcast but my mum says the sun can still burn you through the clouds so I immediately apply a heavy coat of factor 50. Sure, I’m only walking from the terminal to the taxi but I’m taking no chances.

There is great poverty in Vietnam. I know this because I can see some of it through the tinted windows of the air-conditioned 4x4 that picks us up. We are doing this trip in style and this makes me feel guilty. Will I get a true taste of Vietnam if the only locals I meet are the ones carrying my bags to my hotel room? I ponder this as my private tour guide hands me a hot towel.

The trip into the town is hair-raising. There are 85 million people in Vietnam and 21 million motorbikes, all of them honking furiously. Life is lived on a moped. I see one piled high with chickens in hutches. On another, two men are balancing a six-foot pane of glass. Entire families travel on one scooter, Mum clutching the baby while Dad steers. No one pays attention to road markings, and crossing the street is like a game of Frogger. Our guide says you should just walk confidently across the road and hope the mopeds weave around you. I don’t like this idea and wait for a break in the traffic. I wait 15 minutes.

We are on a whirlwind tour of Vietnam and Cambodia. We want to see as much as possible in two weeks, so the tour company has organised a sort of travel taster-menu of the two countries. There is so much to cram in that we’re barely off the plane and we’re at a traditional water puppet theatre (imagine a U-rated Punch and Judy show performed in a learners’ pool), paying homage at Ho Chi Minh’s atmospheric mausoleum (where the revolutionary leader is now embalmed like Lenin) and then holding on to our hats for a rickshaw ride round the city. (In an effort to look cool on this trip, I have bought myself a Mod-style pork-pie hat. I think it makes me look like a hard-bitten war reporter or perhaps Tom Waits. Claire says I look like Farmer Barleymow from Bod.)

The guidebook says you can eat safely and cheaply from the many street kitchens. These are basic, open-fronted shops where an old lady cooks on a simple stove on the pavement while the customers sit inside on plastic garden furniture. We wander the Old Quarter and take our chances. I am wary of foreign food. There’s no menu: each street kitchen serves either pho (noodle soup) or bun cha (char-grilled pork served with noodles and a green salad). We plump for the latter and it’s tasty, although I avoid the salad. (My mum says the salad might be washed in tap water, which will kill me.) I ask for the bill and the teenage waitress charges me 110,000 Vietnamese dong. This seems an awful lot (though it’s actually only £3.50) but I pay up because the free Daily Mail on the plane reminded me that all teenagers want to murder me, particularly foreign ones.

When I’m abroad, money is a constant concern. I lie awake worrying about how much I should tip people. Who do I tip? How much? How do I do it? Do I put it in the palm of my hand and surreptitiously slip it into theirs? Or do I pop it into their breast pocket, smile and pat them on the head? (Don’t do this - it can seem patronising.)

I am confused by the exchange rate. I tip our driver $40. Later, I discover that $2 is the norm. I decide to go back and ask the driver for $38 in change but Claire won’t let me. ‘Great,’ I say. ‘He’s going to tell his mates about the rich bloke with the hat like a Flowerpot Man and every taxi driver in town is going to be expecting a $40 tip. I’ll be ruined.’ I am not ruined, as no one ever mentions it. Also, from now on I make Claire do all the tipping while I pretend I have no money.

From Hanoi, we take a three-hour car journey to the coast, where we board a luxury replica Chinese junk for an overnight cruise in the tranquil waters of Halong Bay. This is our first taste of truly breathtaking scenery. The bay is famous for the thousands of monolithic limestone islands that jut up from its calm waters. It’s a tourist hotspot but apart from a few other junks that chug past in the distance, the waters are serene and silent. You can’t beat the romanticism of a barbecue on deck as the sun sets. The boat is beautifully designed and nearly everything in your room is for sale. I buy the picture that’s hanging above the loo. It’s a lovely old print of Halong Bay that in years to come will be a wonderful reminder of that loo.

Next we make our way down to Hue in the central provinces, a charming, restful little town where we spend a night in La Résidence, a stately hotel that was formerly home to the French governor. The French colonial style is scattered throughout Vietnam, evidence of the years of Gallic meddling in the region, and it’s hard not to feel guilty as our car rumbles past corrugated iron shacks before depositing us behind the walls of yet another gorgeous hotel dripping with imperial splendour.

To appease our guilt we check our Rough Guide and read about a recommended local restaurant called Lac Thien, run by a ‘deaf-mute family who communicate by sign language’. Perfect, we think, and book a table.

We take a rickshaw to the restaurant and as we pull up, a waitress spots our guide book and greets us. As we sit down, a young girl at the restaurant next door beckons to us and shouts in broken English: ‘No, we are deaf-mute, we are deaf-mute.’

I am confused and start to make my way towards her. The woman at the first restaurant says: ‘No, you booked table with us,’ and urges me to sit down. ‘I have the wrong place,’ I say, but quick as a flash she responds with: ‘No, right place. My father also deaf.’ She points to an old man. I suddenly realise that there are two identikit restaurants right next to each other, both with similar names, both with signs saying ‘Run by deaf-mute family, as seen in the Rough Guide’. Obviously one is legit and one is an imposter, cashing in on the other’s guidebook reputation. But which is which? We plump for the first restaurant as we’re already sitting at a table.

Next door, an old man is pointing at his ears and his empty restaurant. I feel guilty. Have I made the wrong choice? I don’t know what to do. Am I allowed to do a quick test on the old man in the restaurant I’ve chosen to see if he’s actually deaf and mute? I think about ordering food from him and then as he turns away, shouting ‘Oy, old man’ and if he turns around I’ll have him bang to rights. Then I remember this is how the Nazis caught out Gordon Jackson in The Great Escape shortly before gunning him down. And my mum says it’s rude to use methods formally employed by the Gestapo. So I just sit down and order my food.

It quickly becomes apparent that I’ve chosen the wrong place. As I eat my food, I can see the genuine deaf-mute father and daughter next door signing to each other in their empty restaurant, while my waitress shouts orders to her father, whose ears are clearly working fine. More guilt. I should have known something was up when we were able to phone ahead and book a table at a deaf-mute restaurant.

Next morning we are taking a cooking class in the balmy gardens of the hotel and are whisked to a local market to admire ingredients. I am taking a photo of some big eels when I notice a few stall-holders are laughing. ‘What are they laughing at?’ I ask our guide. ‘You,’ she says. It turns out a man who is 6ft 7ins tall is quite a novelty. Toothless old men and tiny ladies start running up beside me to compare heights then dissolve into fits of giggles. A man who appears to be a postman starts doing a funny lumbering walk like Frankenstein’s monster, then pointing at me. The entire fish section bursts into hysterics. Soon the whole market is openly pointing and laughing at me. People are calling their friends on their mobiles and telling them to come down. I think I hear someone say ‘Barleymow’.

At one point, a woman actually darts up behind me and attaches the Vietnamese equivalent of a playground ‘Kick Me’ sign to my back. While I scrabble to remove it, like a dog chasing its tail, there are more shrieks of laughter. This is not how it’s supposed to work, is it? Dammit, I thought The Observer sent me on this trip to laugh at the funny foreigners, not the other way round. I race back to the hotel and vow to write something mocking about their hot towels. That will teach them.

After a brief stopover in quaint but touristy Hoi An, we have two very welcome nights of R&R at the Six Senses Hideaway in Ninh Van Bay. Reachable only by speedboat, it’s an idyllic private beach resort with eco-friendly designer villas blended into the hillside. If you were a deranged James Bond villain, you would choose this place as a front while you built your missile silo in a nearby volcano.

At the Six Senses, your every whim is catered for by your personal butler. Personal butler! We have a private barbecue cooked for us on the beach in front of our villa by three men. Three men! I should feel really guilty but I’m too busy wiping meat juice off my face. The head chef ends our evening by performing magic tricks while we eat dragon fruit. It is decadence on a mammoth scale. I return the favour with a quick card trick of my own. The chef looks impressed, and I like to think he now talks of the mysterious magical giant who once came to his island. However, he’s not a simpleton; he’s a trained professional. He probably remembers me only as the greedy giant who ate so much he had to take his trousers off.

We go to bed but I get unnerved by the animal noises outside and the sound of rustling in our room. Next morning I find a giant beetle under the bed struggling on its back. It looks deadly. Or completely harmless. It’s hard to say. I do the manly thing and run to breakfast while my butler disposes of it.

We leave the paradise of the Six Senses Hideaway for the metropolitan buzz of Ho Chi Minh City (formerly Saigon) but it’s a brief overnight visit as the next morning we board a tiny plane for Cambodia.

As we sip beers under the whirring fans of the Foreign Correspondents Club and look out over Phnom Penh, it is hard to imagine that in 1975 this entire city was evacuated and the population moved into enforced labour camps in the countryside. While Vietnam remains poor, it has had several decades to clear away the debris of war and build up a thriving tourist industry. In neighbouring Cambodia, violence and bloodshed stopped only in the past 10 years or so. Pol Pot’s Khmer Rouge were still operating as a guerrilla movement well into the 1990s.

With the Khmer Rouge now disbanded and a relatively stable government in place, the country has done an impressive job of plastering over the tragedy and unrest of its recent past. Phnom Penh is full of bustling street-cafes and tourists in rickshaws visiting the glittering royal palace. The people are charming and friendly but behind the facade the country’s scars are still there. The Killing Fields are now gruesome tourist destinations and Toul Sleng prison, a former school that became a place of torture and death under the Khmer Rouge, is now a museum. It’s a chilling and deeply moving place with hundreds of haunting photographs of the victims hanging on the walls.

Everyone you meet has their own story. Our tour guide cheerily tells us his extraordinary tale of life under the Khmer Rouge and it’s as gripping as any Hollywood thriller. We’re so enthralled we send the taxi round the block a few times until he’s finished.

We had hoped to take a boat up the Mekong river to Siem Reap but the water level is too low so it has to be a short aeroplane flight. At Siem Reap we are picked up from the airport in a vintage stretch Mercedes that used to belong to King Sihanouk. Left to rust during the Khmer Rouge period, it was rescued by the owners of our hotel, Amansara, which was formerly the king’s residence: he entertained the likes of Jackie O here in the 1960s.

Under Pol Pot it became a weapons dump and was left to ruin. Now it’s been restored to its former glory and is the very model of elegant 1960s designer chic. Private butler, private plunge-pool, free cakes and mini-bar - outrageous luxury and our home while we visit nearby Angkor Wat. No words can do justice to the beauty of the vast 12th-century temples so I won’t even try. Just look at the pictures. And try not to be too distracted by my amazing hat.

Tourists flock to these temple complexes, so we get up at 6am and spend an hour or so exploring them with only a blissful soundtrack of local wildlife. I am terrified of getting bitten by a mosquito because my mum says I will get malaria and die. I cover myself in a thick sheen of insect repellent. I want to bring a mosquito net with me from the hotel but Claire says it will look silly with my hat. As other tourists start to arrive, we venture down a jungle pathway and 20 minutes later find Ta Nei, a smaller temple rarely bothered by visitors. It’s private and beautiful. I need a wee. I am about to go behind a tree when my guide reminds me that there are still between 4 million and 6 million unexploded land mines in Cambodia and I should be careful where I tread. I hold it in.

Next day we take a boat ride on Tonle Sap lake and stare at the families of fishermen who live on the water in floating villages. This makes me feel guilty again. I am peering at poor people like they’re animals in a zoo. I am disgusted with myself so I make sure I’ve got enough photos and then ask the boatman to take us back. This is the agony of holidaying in developing countries. Some say you are bringing welcome cash into the economy, others that you are exploiting the impoverished locals. Have I seen the real Vietnam and Cambodia? I haven’t ventured off the tourist trail, so not really, but if you’re like me and you want to see far-flung places without getting your hands dirty, it can be done, and in great style and safety. And even if I wasn’t very adventurous, one evening after dinner I did utter the words: ‘Hmm, I think that gekko is repeating on me.’ Now you can’t say that after two weeks in Devon.

· Stephen Merchant’s BBC Radio 6 Music show is on Sundays, 3pm-5pm.

Essentials

Stephen Merchant’s trip was tailor-made by Bales Worldwide (0845 057 0600; www.balesworldwide.com). His 15-day itinerary costs from £4,495 per person based on two people travelling together and sharing a double/twin room, including return flights on Thai Airways, all internal flights with Vietnam Airways, guided sightseeing, some meals and all accommodation, including a two-night stay at the Six Senses Hideaway, Ninh Van Bay, one night at Raffles in Phnom Penh, a three-night stay at Amansara in Siem Reap and one night at the Raffles Grand Hotel D’Angkor.

Bales also offers an 11-day ‘Mekong Odyssey’ escorted trip from £2,165, including two nights in Ho Chi Minh City, a visit to the notorious Cu Chi Tunnels, a river boat trip down the Mekong Delta, Can Tho, Chau Doc on the Cambodian border, two nights in Phnom Penh and three nights in Siem Reap and the Temples of Angkor.