Sir James Dyson would make a good therapist for anxious Brexiteers. Everything about him is comfortingly precise — his manner and way of speaking, his owlish round glasses and blow-dried white hair. He exudes a Zen-like calm.

What he has to say is reassuring, too. He is as sunnily optimistic about leaving the EU as he was before the referendum last year.

‘I am very confident,’ he says, ‘in our ability to negotiate trade deals outside Europe — with Japan, Australia, China, America and so on — because it’s very easy. It’s just us negotiating with them. It’s very, very straightforward and you don’t have to satisfy 27 other people.’

The implication is that a deal with the EU will be harder. He confirms: ‘My view is we almost certainly won’t get a deal. We’ll have to walk away.’

But Dyson doesn’t think that matters. Falling back on World Trade Organisation rules would be ‘no big deal’, he says, because for him it would just lead to a 3 per cent tariff. ‘Frankly,’ he says, ‘lowering corporation tax a few percentage points would pay for that.’

We meet not at his technology company’s swanky headquarters in Wiltshire but at a place that he has kept very quiet about until now — his farm, or one of them to be precise, in the depths of rural Lincolnshire.

Near the farm, shiny new lorries are powering along the road with Beeswax, his farm company’s name, emblazoned on the front. They wouldn’t look out of place in the American Midwest. His total farming estate, I learn, is the biggest in the UK, encompassing 33,000 acres in Lincolnshire, Oxfordshire and Gloucestershire. The Spectator is the first publication to be shown round.

In many ways, Dyson the farmer is returning to his roots. ‘I was brought up in Norfolk and I worked on a lot on farms, picking potatoes, topping Brussels sprouts, rushing parsnips to the Campbell’s Soup factory,’ he says. But farming is a tougher gig than it was back in the 1950s and 1960s, when, he says, farmers ‘were quite rich’. Profits have been squeezed for decades and it’s very often loss-making, as Dyson’s farms have been recently — they lost £4 million last year and expect to lose £2 million this year.

Luckily, he can afford it. According to the Sunday Times rich list, Dyson is worth £7.8 billion. ‘I don’t want people to feel sorry for me,’ he says, as if that were a real danger, ‘because I am making money in my other areas.’ When he shows me a state-of-the-art grain storage later, he jokes: ‘Hairdryers paid for that.’ He has poured £75 million of his own money into his farms (not including the cost of buying the land) to improve them agriculturally and for wildlife. This is not a business loan — he won’t get any of it back. You might call it environmental philanthropy.

Which is why he is a bit cheesed off — to put it mildly — with Michael Gove, the new Environment Secretary. He sucks his teeth and grimaces slightly at the mention of Gove’s name. It might have something to do with the Environment Secretary’s recent interview on The Andrew Marr Show, when he was asked if ‘very, very wealthy farmers… like Sir James Dyson’ will get less money after Brexit in the form of government subsidies. Gove’s one-word answer was ‘Yes.’

Dyson had met Gove a few times and says he was pleased with his appointment because ‘he is articulate and speaks out and gets publicity’. But, he adds drily, ‘we just need to get the right speaking out and the right publicity’.

This, it seems, is why I have been invited to tour the farm: not just to see what Dyson is up to, but to hear why Britain’s farmers need subsidies to continue after Brexit — even if they are very, very rich.

The sheer scale of the Dyson farms is difficult to grasp. We drove round the Carrington estate for an hour in a Land Rover and saw only a tenth of it. But he proudly reels off some figures that help put it in context. The farms produce 25,000 tonnes of wheat per year, 4,500 tonnes of peas (if you ever buy peas at Waitrose, they are almost certainly his), plus potatoes and other crops. They include nearly 100 miles of hedgerows and ditches. One of the biggest outlays so far is the fortune — about £5 million — spent on improving drainage, which isn’t subsidised.

It’s strange to hear one of Britain’s richest men talk about the drainage in the lower field, like Ted the estate worker in The Fast Show. But Dyson is an engineer to his fingertips. What gets him excited, visibly, is making things and practical problem-solving. I am shown a great big hole in the middle of a field, recently dug. Here clay drainage pipes, installed in the 1950s and now all clogged up, are being replaced with new plastic ones. This is the kind of muddy project, along with the clearing of ditches and dykes around the farm, which will prevent a flooding disaster like the one that hit Somerset in 2014.

The development that he really wants to show off is an anaerobic digester, a futuristic thing that looks like a giant Dalek. Using the gases produced by rotting crops and waste food (including a Kilimanjaro-sized pile of onions), it drives a turbine and provides renewable energy for more than 10,000 homes. In fact, it’s cleverer than that: surplus heat and power are used to dry grain. And the digested crop is put back on to the fields, which boosts growth more than any normal fertiliser.

In other words, Carrington is a high-tech farm that can’t get much more efficient. The farmers and workers I meet speak like expert technicians. One of them is a qualified drone pilot, who works with outside contractors to spot weeds, and nesting marsh harriers, among the crops. The drone’s data card is then inserted into a self-driving tractor which sprays only that area of the field, rather than the whole crop, with whatever treatment is needed, or steers round the rare birds. An H.E. Bates novel this is not.

There are benefits of farming at such scale, though not many. You can invest in the best machinery. When it’s raining on one bit of the estate, you might be able to go elsewhere to harvest. You can rotate crops and never run out of room. And yes, Brussels gives you lots of money. Greenpeace recently reported that Dyson’s farms received £1.6 million from the Basic Payments Scheme, which is part of the EU’s Common Agricultural Policy. It’s a big cheque. But Dyson claims the revenue is much less once you take into account the cost of obeying EU rules.

Then there is the separate UK Environmental Stewardship scheme, which provides grants but means Dyson has to set aside about 2,200 acres for ‘flowers, seeds, nesting birds, archaeological buffer strips and so on’. He is very happy to, but that means foregoing income of about £640,000 a year. Dyson’s argument, in short, is that the subsidies aren’t just free money.

This doesn’t sound like a complaint so much as a pained observation. If Dyson, a billionaire, can invest tens of millions in his farms, and still not make them profitable, what hope does a smaller farmer have, with far few resources, especially if government subsidies are to be slashed after Brexit? Farmers wouldn’t have the money to prioritise the environment, he says, and in terms of produce, ‘You’ll be putting British farmers at a disadvantage against European farmers.’ Who, of course, will carry on being subsidised by the EU. It is very easy for a supermarket to buy potatoes from Holland or Hungary if they are cheaper.

By instinct, Dyson doesn’t like subsidies or tariffs. ‘For someone who believes in free trade that’s a bitter pill to swallow,’ he says. But he argues that ‘we have become as efficient as we can’, because the soil can only give so much. So either you have government help, or farmers go bust. If

chlorine-washed chicken, acid-washed pork and hormone-injected beef starts coming from the US, tariff-free and cheap, farmers will be in real difficulty. In particular, he says, ‘cattle farmers would just have to give up’.

This could lead to a kind of Corn Laws 2.0 showdown — British landowners vs supermarket customers, who might actually quite like cheap American imports, chlorine or not. Will Gove be brave enough to take the side of farmers?

But even now smaller farmers are ‘horribly vulnerable,’ says Dyson — to bad luck, ill health, weather, currency swings and fluctuating international prices. Even if they are selling what they grow, they get only a very small slice of the cake. He hopes one day that the route from field to dinner table will be quicker and farmers might be able to cut out the middle men.

Whatever Michael Gove’s ‘Green Brexit’ turns out to be, Dyson is going to be the farmers’ friend throughout the process. ‘I hope I’m representing all farmers,’ he says.

Dyson looks at his farm as a 50- or 100-year project that will outlast him. His grandchildren, he tells me, have visited the farm and ridden on the self-driving tractors.

For now, it’s a passion as well as a business. ‘I like making things,’ he says. ‘I’m an engineer — farming is very analogous to that. It’s wonderful seeing crops grow and lorry loads of peas go out. It’s what I do.’