Sam Neill is an oenophile and vigneron: two words that strike cold terror into the Observer's bean-counters in advance of our lunch at St John in Clerkenwell. These fears are not allayed by the 66-year-old actor's rather jolly Twitter feed, which for the week before today's encounter has detailed the adventures of an assiduous bon vivant, matching food and fine wine in some of London's smartest restaurants. "Try to steer him towards the less expensive bottles," suggests my editor.

At the appointed hour, Neill bounds up the stairs to the dining room in the whitewashed one-time smokehouse. His hair is neatly parted at the side and a clipped moustache bristles: the effect is of a second world war officer on leave. As he takes a seat at our table, he smooths the paper tablecloth with his hands, clearly delighted to be here. This is not, it will turn out, because of the opportunity to hold forth on a long, fruitful career that has included star turns in Jurassic Park, The Piano and, recently, the ambitious BBC drama Peaky Blinders. He has little more than cursory pride in those achievements. Rather, Neill loves St John and eating at the restaurant – especially on someone else's dollar – is never a hardship. "I've been coming here for almost 20 years; I'm obsessed by it," he says. "I like paper on table. I like rooms that are painted white. I like food that says what it is and no more. I like British food, which is mostly terrible, but when it's good it's fantastic." Neill pauses as a waiter drops off a pair of menus and a wine list, and for a few seconds we've lost him. "Oh my God, I just want to eat everything. Beef mince on dripping toast! That's just fucking great, isn't it?"

Eventually, his gaze shifts to the wine list and his lip curls like a king unamused by the entertainment. "Let's talk about this," says Neill, jabbing the A4 sheet with his finger. "This is the one terrible blind spot of this restaurant. Look at this wine list: 100% French! That's like going to a really, really great travel agent and the only place they'll send you to is the Balearics: 'That's it, whatever you want, but you can only go to Ibiza.'" Has Neill ever had a conversation with Fergus Henderson, the owner, or anyone else at St John? "I have," he replies. And how would they defend their policy? "They'd say, 'Do we look like we give a fuck?'"

The waiter returns and Neill collects himself: he orders a bowl of peas followed by the mince on toast ("Just because I can"); I join him on the main course after an asparagus and hot butter starter. "And I'll have a glass of wine, even if it is French," he decides. He scans the list and the left side of my chest (either my heart or my wallet) beats a little quicker. St John has a serious selection rising up to the 2000 Chateau Mouton Rothschild at £2,150, but, in the event, the Observer needn't have worried: Neill selects a red from Languedoc called Mal Aimés at £8.50 a glass. "I'll drink anything," says Neill. "So I can get drunk here reasonably effectively. But when you get to my age you realise you've only got a certain amount of drinking years left, so you may as well invest in something good. A handmade suit or a handmade wine is a whole new dimension to being alive and living well. I'm not necessarily talking about luxury: luxury is bullshit, but quality is an entirely different thing."

Neill was born in Northern Ireland, where his Kiwi father was stationed with the British army, and boarded a boat to New Zealand when he was seven. He had been christened Nigel, but aged 10, bored with the bullying, adopted a new identity: Sam. This allows Neill to be boisterously dismissive of Ukip's Nigel Farage: "That man will never make it to the top," Neill wrote in a recent diary for the Spectator, because of his "fatal name". Our starters arrive and, just like the menu said, Neill gets a bowl of unpodded peas tossed like pick-up sticks. He laughs, "Takes me back to my grandmother's garden."

Adroitly stripping a pod, guzzling the peas, Neill continues: "My whole career has really been one of surprise. I never expected to have a career on screen. It snuck up on me." He suffered from a stammer as a child – was it related to that? "No, it's to do with living in a very small place. I was a very small fish in a very small pond. There were no precedents. No one in New Zealand ever had a film career."

Neill's breakthrough year was 1993, when both Jurassic Park (the highest-grossing film ever at that time) and The Piano (three Oscars) were released. A natural choice might have been to follow the job offers to Hollywood; instead he chose to buy land in central Otago, in the heart of New Zealand's South Island, with a view to starting a vineyard. The country was already starting to receive good notices for its sauvignon blancs, but there was scepticism that any decent grapes would flourish so far south. Neill and others concentrated on pinot noir, a fast-growing grape that is happiest in cool conditions, and he now has four small plots – including one that is probably the world's most southerly vineyard – which are known collectively as Two Paddocks.

"It's interesting you say '93," reflects Neill, "because I probably had a bit of disposable income then, which made it possible to establish the vineyards. What I hadn't realised was that it would eat up all my disposable income for the rest of my life."

A towering, unctuous mound of beef mince is brought, and Henderson stops by for a chat. Neill decides not to admonish him (again) for his wine list, but they have a cheery conversation about comfort food, and Neill says he will probably see Henderson again next week when he is coming back to the restaurant with his friend Timothy Spall. "He has just won best actor at Cannes [for his role in Mike Leigh's Mr Turner]," Neill notes, proudly. "It'll be his first public appearance since then."

Growing wine, Neill believes, has made him more phlegmatic: the entire crop at one of his vineyards was wiped out by a night of unseasonably late frost last November. "Something of a heartache," he says. "I'm at the whim of a capricious God." His passion for wine-making has also led him to reassess his day job, largely because he finds it hard to leave his grapes, especially during harvest for his vintage wine. Wiping mince from his moustache, Neill says: "With acting, I just wait for the phone to go. If it doesn't go, I've got other things to do. When I'm at home, I don't even think about work. I love a great movie, but I hardly ever go to the movies. Most films I see are on aeroplanes. It's a terrible admission but it's true."

Returning for another series of Peaky Blinders was, however, no hardship. "Writing like that is a bit of a rare thing," says Neill. "I read the first episode, rang my agent and said, 'This is amazing.' I didn't even read the second episode." His part is that of Campbell, a sadistic policeman from Belfast brought in to clean up the gangs of Birmingham in 1919, specifically the Peaky Blinders led by Cillian Murphy's Tommy. At the end of the first series, there was a cliffhanger over whether Campbell had survived – evidently he did. "Oh," says Neill, looking like he's trying to remember the official line, "there was never going to be a second series unless people liked it."

Neill doesn't really have time for dessert, but he decides to make some. He'd seen a dish called apricot cobbler on the menu earlier and is determined to find out how it differs from a crumble. The answer, we're told, is that the topping is closer to scone dough, which appears to delight Neill no end. As we wait, he reflects again on how his career might have been different if he had moved to Los Angeles. "The other thing that is regrettable about America and one reason not to live there is that they tend to put cinnamon in every possible pudding," he says. "I just think that's disgusting."

The cobbler is gobbled, the bill arrives and Neill stands to leave. "Is the Observer doing this?" he asks. I nod.

"Good shit."

Series two of Peaky Blinders airs on BBC2 in the autumn. For more on Two Paddocks wine visit twopaddocks.com