The BLU-26, the most commonly found cluster bomb in Laos, is a tennis ball-shaped bomblet designed for maximum damage. Children who have seen these relics made into lamps, table legs or even cowbells find them irresistible to play with, and often die or are maimed as a result.
"Landmines just upset me," says Wilson, who is travelling in Laos with the charity Landmine Action. "The idea that they're aimed at an innocent population to maim and drain the economy is a putrid idea. How can people go to bed at night knowing they've produced them, or bought shares in armament companies?"
His purpose here is to focus attention on the cluster bombs and other unexploded ordnance. Between 9m and 27m unexploded cluster bomblets are "seeded" throughout the country, a pernicious reminder of America's mass bombing of Laos during the Vietnam war - an assault kept secret from the rest of the world. A quarter of a century later, people's lives are still being ripped apart by it. Innocent pastimes, such as hoeing a field, throwing stones into a river or lighting a fire, can have fatal consequences. Since 1973, 12,000 Laotians have been killed or maimed. "The problem," says Wilson, "is that no one will take responsibility. The Americans spent over $2m a day on the bombing of Laos, now they're only spending $2m a year to help clear it up."
Even in the furthest outreach of the backpackers' trail in Phonsavan, the dusty capital of Xieng Khouang (the most bomb- saturated province of Laos), Wilson can't get away from the business of celebrity. In the bustling Sangah restaurant - frequented by expats, travellers and roving Chinese road builders - an English student approaches, sheepishly: "Am I right in thinking . . . ?" "Yes, you are indeed right," Wilson replies, slowly and deliberately. Later the man returns with 13,000 kip (£1.30) from his depleted budget: a donation to Landmine Action.
Overseas charity trips seriously test tempers. There are endless briefings, long journeys on punishingly uneven roads, few or no creature comforts and ever changing itineraries. I had assumed that by travelling for eight days with Wilson, I would come away with some compelling insights into the 65-year-old actor. However, Wilson is so contained, restrained and mindful of the slightest indiscretion (always followed by a quick "off the record") that my most staggering revelation involves his partiality to cold baked beans, which he keeps in his fridge ready to liven up a salad.
He is prepared to answer questions on any of the following subjects: politics (he is a strong Labour supporter); theatre (he is an associate director of the Royal Court, for whom he directs one play a year); youth (he was rector of Glasgow University in the late 90s and an ambassador for VSO); the royal family (he is not a fan); the supernatural (he dismisses the notions of ghosts, horoscopes and UFOs), religion (he can't believe how intelligent people join the clergy). But he never asks questions back, and has a knack of moving the focus of the conversation to the middle distance.
Baked beans aside, Wilson doesn't see any inconsistency between his socialism and his predilection for the high life. He likes to travel first class, hires limousines for the day and has a masseuse come to his house once a week. "I'm not particularly proud that I enjoy these things, but why not?"
In Laos, the curmudgeonly Victor Meldrew only occasionally puts in an appearance, and always with irony - for instance when he hands out a packet of mints to the dry-mouthed assembled group and everyone takes one. "Well, that was a mistake," he says, cocking an eyebrow at his suddenly three-quarters-empty packet.
He is game for almost anything. When it turns out that we have to fly on a dodgy Chinese plane which lurches from Phonsavan to Vientiane instead of the spanking new French model, he shrugs. "I'm not usually scared of flying, but I was then," he later admits. Visiting the 2,000-year-old Plain of Jars, he agrees to pose for a photograph, placing himself gingerly inside one of the massive stone jars, with just his head poking out.
For such a self-possessed man he is surprisingly considerate of other people's feelings, worrying, for instance, that a solitary backpacker sitting at the end of our table "wants to talk". At the end of the meal he goes up to chat. What he dislikes is people being nosy - like the English woman at Vientiane's sleepy airport who started talking in a very loud voice as if he was a long-lost friend. "But I'm meticulous about trying to be responsible. I know it's the public who made me famous, and I owe them something."
He is not sorry to see the end of One Foot in the Grave - although Victor is making a one-off comeback for Comic Relief. "I'm relieved to see the back of him," says Wilson. "I'd played him out and there was no challenge any more." Nor is he too worried about the future. He has just finished recording High Stakes, a comedy series for ITV in which he plays a merchant banker, and is about to start on another series with Stephanie Cole for the BBC.
One of the privileges of his fame is getting access to projects and places about which he cares passionately - for instance, the rehabilitation units in Phonsavan, where amputees are fitted with prostheses. "I've always had a terror of having a bit chopped off," he says. "It's the body-image side I find quite disturbing."
The cluster bomblets cause mainly upper-body injuries - blindness and hand amputations. Many victims cannot afford surgery and long-term antibiotics, and simply die. Amputations and deaths also occur because villages are inaccessible and roads impassable. One seven-year-old boy's foot burned for eight days because there was no running water.
Visiting a school built on bombs and watching a clearance team in operation, Wilson quickly gravitates to the kids. "I love children," he says. "They're so unadulterated and open. Unfortunately they don't always stay that way. It's sad when they grow up too quickly and become manipulative, skiving and contrived."
Wilson's words could just as well apply to the perpetrators of the cluster bombings who have failed to clear up the lethal mess they left behind in Laos, Iraq, Kosovo and Kuwait; or, for that matter, to the British government, which still refuses to implement a freeze on such obscene weapons of war.
Contact Landmine action on 020-7820 0222 or at www.landmineaction.org. The One Foot in the Grave special is showing as part of Comic Relief, 7pm, Friday, BBC1.
