‘Smell this!” Chef and wild food enthusiast Nurdin Topham is inhaling a lungful of shrub called pineappleweed, picked fresh from a stretch of east London formerly known as Murder Mile. He hands me a couple of yellow buds with an instruction to sniff; sweet fruitiness floats under my nose. Topham takes a chew. I gamely follow suit. The clue, it seems, is in the name: we’re eating what vaguely tastes like pineapple and feels a lot like chewing grass. “This is food,” he explains, as we ramble on, to forage for a lunch he will be cooking later.

The future of food and our relationship with nature is at the core of Topham’s philosophy for what he calls “nourishing gastronomy”, a subject he will deliver a lecture on this week at FutureFest in London. He has two decades of experience in the field, first as a qualified nutritionist and personal development chef for Raymond Blanc, and later as head of NUR, his own Michelin-starred restaurant in Hong Kong.

Nurdin Topham plucking flowers along the canal. Photograph: Sophia Evans/The Observer

“Wild food is about connecting to our ancestors and to the earth we’re living on,” he says, as we tramp past the early morning joggers and dogwalkers of the local park. “It’s a struggle living in the city – I long for a more outdoors life – but picking food in an urban setting helps.”

Although he was born in London, Topham grew up, I’m not surprised to learn, surrounded by rolling fields, forests and orchards in the Brecon Beacons. His father, Anthony “Top” Topham, who was the lead guitarist in 1960s band the Yardbirds before Eric Clapton joined, converted to Islam and moved his young family to the good life, where they had a Muslim upbringing, grew their own food and made their own jams.

Nurdin’s first wild food experiment was with nettle soup, made outdoors in the dark with his best friend, aged around eight or nine, and hastily gulped down. “We proudly took it indoors to show our parents – under the light we discovered it was crawling with caterpillars.”

Since then, he has managed to poison himself twice but also to establish himself as an authority on cooking more closely with nature. “I wouldn’t force foraging down anyone’s throat,” he says, by way of joyful apology.

‘I wouldn’t force foraging down anyone’s throat’, says Nurdin Topham Photograph: Sophia Evans/The Observer

We pause to peer at some unidentifiable green. Is it brassica? Mugwort? Topham whips out his phone and takes a picture to upload to PlantNet, the app designed to help users identify what they’re looking at. Inside his bag is a trove of plant tinctures (essential oils he has made and labelled himself, extracting the essence of a range of plants and herbs), some homemade kombucha and a load of food bags.

“I shouldn’t be using all this plastic,” he frowns, “I should have bought my tins.” He pops the mugwort in anyway.

Dorkily, I ask if we’re allowed to pick, willy-nilly, across the city.

“Yes, this does bring us on to some of the ethical dilemmas of plants and where you’re picking from…” Another sighting of pineappleweed snatches his attention.

“This wouldn’t be the ideal place to pick anyway,” he says, motioning towards the weeds sprouting through pavement cracks.

“It’s where people are treading through and dogs are pissing, but you do get to learn a lot. For instance, it helps you realise that there aren’t four seasons: when it comes to plants, you can have several seasons in a week. And that’s what’s really special for me. A dish I make is never static; it’s also constantly evolving.”

In Hong Kong, Topham invested serious time in setting up a supply chain directly with local farms “to source deliveries three times a week – which is a headache in an area where 94% of the food is imported – just so we could pick plants and use them for a short period of time”.

The plants foraged from the marshes ready for salad creation. Photograph: Sophia Evans/The Observer

It’s because of this that NUR earned a reputation as “the most innovative restaurant in Hong Kong”, according to Forbes, and a rave write-up for Topham’s “absolutely flawless cooking” from Frank Bruni at the New York Times. So what, for him, makes plants so important to his cuisine?

“They’re our medicine! That’s an obvious thing to say, but their deliciousness is important, too.”

Topham is especially keen to bring “food democracy” to the UK and help develop a culture where, as in Japan, “a delicious bowl of noodles can be had for a fiver”, and there is an emphasis on the link between nutrition, health and taste.

But isn’t urban foraging a bit of a middle-class indulgence? “Oh yes, I’m not suggesting everyone has the luxury of time to forage – that is a luxury. People are out there working, living in cities, struggling to pay rent and bills, keep a roof over their head and buy food which has gone up incredibly in price over the past few years.”

But, he says, “as mental health is such an issue these days, to get out for a walk in the countryside is a fairly nourishing thing for people who can’t connect to a sense of calm and still. It’s natural aromatherapy from being among blossoms and breathing deeply.”

We arrive under a bridge by the canal, mostly used by runners, dogs and narrowboat owners. So far, we have a haul of leaves – sorrel, something cabbagey, ragwort. This patch doesn’t look promising, I suggest. Topham emerges with bunches of wild, peppery rocket which taste nothing like anything that would ever emerge from a supermarket salad bag. “It tastes alive,” he munches. It’s rocket amped up to 11.

Satisfied, we head to Carousel, a central London restaurant where Topham is resident chef for a week and is to convert our haul into lunch. There is an element of cheating – we didn’t catch the mackerel or harvest the watermelon, but Topham says our morning of picking and chewing in the park is just one element of bringing a dish together. Unsurprisingly, his meticulously presented dish is a hit.

Nurdin Topham’s foraged salad Photograph: Sophia Evans/The Observer

“We’re good at keeping pace with changes in the UK, and people are interested in food now,” says Topham. “Ten years ago, you wouldn’t have heard men in pubs talking about food. It wouldn’t have happened and that’s a massive change. Thanks to people like Jamie Oliver – whom I haven’t met but have such awe and respect for – it has changed. He’s a food warrior.”

For his part, Topham is on the hunt to develop a food lab: to study plants, “to feed people – and not on a £100 a head menu”, and to offer workshops. “I’d like to illuminate and inspire. I don’t like to educate because I’ve got so much to learn for myself. I would like to be in a position where I can facilitate more nourishment and a more humane relationship with food.”

Five to forage

Ground elder

Use it as a herb; like parsley, it pairs well with fish and pasta

Dandelions

Brew the leaves for tea; use the petals for risotto

Rocket

Good for all summer salads

Sorrel

This is at its best in a sharp, citrussy soup

Yarrow

Sweet and medicinal as a dried herb