Buffalo's website lists 40 products, everything from fridge magnets of Clunes with a fish in his mouth (£2.25) to a chocolate "Surgeon's pack" of edible scalpels (£6.99). Mugs reading "Make an Appointment", tote bags and umbrellas are also available. "You can get it all from docmartinstore. com!" says Clunes.
All items, he stresses, are locally produced. "Philippa and Mark Crowdy, our executive producer, have spent a lot of time sourcing. It would be awful to get it made in Nottingham or China. So it's all made in Cornwall."
All of this comes through Buffalo, or more accurately, through Clunes and his wife. Doc Martin Inc is indeed a family business. "One of the crew joked to Emily, 'One day, ma'am, all this will be yours.'"
Yet if Clunes makes it sound like a cottage industry, Doc Martin is also a hugely successful global commodity. The show's version of a particularly British idyll has been sold to 208 territories. This means that every time one of the 39 episodes is shown, Buffalo makes money. The format has been licensed to Spain, France and Germany and is carefully protected by Buffalo.
"We keep it in check," says Clunes, listing certain key elements that must remain in place. "You've got blood phobia, you've got a surgeon who's denied surgery, who has to conquer this but can only work in medicine in this other way; and a man who is a specific type of character - not a cuddly guy.
"I've watched the German version," says Clunes. "It was really funny because they bought our music as well. They did it shot for shot like ours - but in a not-very-attractive industrial harbour town. It was weird with Colin Towns' music, yet German speech, which, at a squint can sound like English with "-en" on the end of each word. 'Comen ze innen and looken arounden.' "But the French guy looks rather comely. I haven't seen him in action, but he's doing well."
Doc Martin has become an export business because all broadcasters love a proven winner. "They're buying something that's been road-tested. And they really do do tests on these things. After the first series we heard the BBC had a team dissecting Doc Martin, a workshop, to find the magic ingredient."
One candidate would be Clunes himself. Ironically, he says, "I don't think Doc Martin would be commissioned now if it was starting. Because telly's moved on in seven years. It has an ageing star." Yet it's still hugely popular. It must make ITV a fortune too?
"Yes it does. But look at what does get commissioned now. They need young Martin Clunes to come through."
Old Martin Clunes is doing just fine at 49. He lives on a beautiful Dorset farm. He owns 14 horses, which, you suspect, are of considerably more interest to him than TV, acting or anything else. Would he be sitting on all that without Doc Martin Inc?
"Probably not. But the Doc Martin millions? That is a myth. It's all tied up in the farm. You have to have a disposable million to be a millionaire. I don't."
According to company accounts, Buffalo made £330,000 gross profit last year. Sales are likely to have been four or five times that. But despite such sums, Clunes is anxious to cast himself and his wife as the opposite of titans of international commerce. If anything, he finds Doc Martin's global success mildly embarrassing.
"It partly makes you want to turn away from it. We've a friend who buys and sells businesses. When he realised we make this programme by ourselves, he said, 'What are you going to do with your company?' We said, 'Not much. We just want to go and ride the horses really.' "
Clunes and his wife insist that, in spite of its popularity, they'll only make a new series of Doc Martin every other year. "We've always had a gap of a couple of years. For Emily's sake, we won't do it every summer. That's the downside for ITV of employing a small family business."
And what if ITV had asked for more series or none at all? "Then we'd have said, 'OK. We'll take it somewhere else.' It's ours. ITV gave me all the chances that I've ever had really, letting me headline things, letting me play Mr Chips - why would you get the man from Men Behaving Badly to do Mr Chips? I owe all that to them. So I'm loyal. But if it ends, I'll do something else. I can always fall back on the farming."