A real catch: The man who is bringing local fish to the capital's tables

Few Londoners know that cod, plaice, bass and even oysters can all be caught in the River Thames

I'm driving in heavy traffic along the A13 towards Canvey Island in Essex. A summer downpour has reduced visibility to near zero and the shock of my five o'clock alarm has only just started to recede. Yet I'm bubbling with excitement. Through a break in the weather I've just caught my first glimpse of the flaming vents and cooling towers of Coryton Refinery. I know that within a few hours I'll be handling some of the freshest seafood in London.

Half an hour later I shake hands with Martin Yorwarth and clamber down a rusting ladder on to his red trawler the Jessie Alice. As a lifelong resident, Martin knows full well that Canvey is best known as a decaying East End holiday resort rather than a foodie's nirvana. But the 35-year-old is on a mission to change this by delivering the foodstuff inner-city gourmets crave most: wild, fresh, locally sourced fish. "People want day-caught fish," he explains. "Good quality fish that's caught on their doorstep. They don't want something landed by a super-trawler that's four weeks old."

Just forget any notion of Martin sailing around a coastal idyll to achieve this. Casting off from a small jetty amid the mud flats of Holehaven Creek, we chug into the Thames Estuary under the sharp industrial gaze of the refinery and are instantly dwarfed by a procession of vast container ships and oil tankers. Under dark, rain-heavy skies the shoreline resembles an aquatic version of Blade Runner, with cranes, fuelling platforms and wooden piers all jostling for position with the refinery's jumbled assortment of pipes and gas flues.

To make things even harder, the waters on Martin's patch are littered with the jetsam of this industrial highway. To navigate the fishing grounds he carefully weaves a path around discarded anchors, sunken barges and countless other camouflaged obstacles. It's only because he's sailed these waters since he was 16 that he knows where the danger lurks. As Martin deftly puts it: "I've had a few close calls [with the tankers]. You basically just give way."

Yet despite history's efforts to ruin the fishing between Holehaven and nearby Stanford-le-Hope, Martin has discovered something special amid the chaos: an ample supply of top-quality, sustainable seafood on the outskirts of London.

After setting his nets and trawling the waters for 90 minutes he brings in a small but impressive catch of crabs, Dover sole, flounder and gurnard. For a seasoned landlubber the sight of a catch being landed provokes a strange combination of awe, excitement and pity. Yet most of it is quickly tossed back alive into the sea – only the largest adult fish are kept.

Pride of place is taken by a large red gurnard. With its sharp, prickly fins and gleaming skin, you'd expect to see it swimming past your snorkel in the Caribbean or Red Sea rather than the back of a trawler bobbing around the gateway to London. But it's by no means alone, as Martin has landed such tropical varieties as parrot fish and fresh-water carp over the years. At different times of the year his more normal catch includes oysters, dabs, plaice, pouting, herring and a little-known salmon delicacy called cucumber smelt.

"Tell people you've caught this so close to London and they won't believe you," Martin shouts with the gurnard proudly held outstretched. "But they've cleaned up the Thames so much now that on a sunny day it can be impossible to trawl because the water's so clear the fish see the nets coming. Over the last 20 years Canvey's water has gone from category C, which is the lowest you can get, to category B. Whitstable is now category A, which means you can eat oysters straight from the sea without having to purify them."

Sadly, there's little time to take this all in. With Lithuanian first-mate Egon Judeikis busily gutting and cleaning the catch, Martin turns the Jessie Alice away from an oncoming container ship and resets the nets.

Over a cup of tea in the cabin he later explains that he's spent years trying to mentally reconcile the fact that most of his fish cannot be landed because of a quota system that means a large section of the UK's catch is "owned" by insurance companies.

In order to keep the cut that normally goes to agents, Martin has now taken the brave decision to ferry his fish direct to farmer's markets around London. Thanks to a new series of night markets in Covent Garden, he's also taking things one step further and bringing his Canvey catch straight into the heart of the capital.

He explains: "I think there's a massive market for this type of fishing. The problem is tapping into it as it's a lot of work to go trawling in the morning then take the fish to market yourself. But it's nice to see both sides of things. Fishing is quite a solitary job and I now get to meet all different sorts of people. Most customers like the thought that it's caught locally, and that they know where it comes from. There have only been a few who've been concerned about the water quality, but once they've tasted the fish they've always come back again and again. After all, it's only hours old sometimes. So the quality is second to none."

But while Martin is introducing London palates to forgotten local delicacies, in truth he's not doing anything new. Two hundred years ago nearby Barking was the busiest fishing port in the country, while fish have been plucked from Holehaven's waters for thousands of years. In many ways, landing fish on the banks of the Thames harks back to a time before edible preservatives, tinned tuna and the invention of the steam train.

Thankfully, Martin both knows this and relishes the opportunity to revive the past by showing that there's far more to the Thames than discarded bikes and burst footballs. Even news that Europe's largest container port is about to be built in the middle of his fishing grounds doesn't phase him. It's simply one more aspect of modern life he needs to adapt to.

"I caught a load of black sea urchins a couple of months ago and we were going down to a market so I thought I'd put them on the side of the stall for some decoration," he chuckles over yet another steaming brew. "From nowhere this French woman came up to me raving about 'Oursin! Oursin!' So I gave her one and she cut it open. Inside it has these beautiful, fragrant eggs. They're really delicious. I didn't have a clue they were there – I've been throwing urchins over the side of the boat for 20 years. So we put them all together and sold them at 50p a go!"

With that, Martin turns the Jessie Alice towards home and brings his nets back on deck. Above us the skies hang black and heavy, and after shaking hands I encounter the same haze of swerving drivers and horizontal rain on the roads.

Yet now I am not alone: in the passenger seat rest a pair of freshly skinned dover sole. I have lived in London all my life, yet this is the first time I've got remotely close to a local fish. Thanks to some flour, a frying pan and some oil, I can happily confirm that it won't be the last. Martin and Egon can now add another name to their list of the converted.

Fish: the freshness test

We'd all like to eat the freshest fish possible, but the truth is that very few people know what to look for at the supermarket or fishmonger's. Here Martin gives a few pointers on getting the best possible produce:

Bright eyes

"Anything that has red, cloudy or sunken eyes is not fresh, no matter what the fishmonger tells you. The eye should look like a healthy dome on the fish's face."

Clear slime

"Rub your hands down the skin of a freshly landed fish and you should find a layer of clear slime on your hands. It should never feel dry or scaly."

Red gills

"Open the gill cover and take a look inside. The fleshy part should be a healthy red, so avoid anything that's either grey or brown."

Sea smell

"Only old fish has a 'fishy smell'. When it's fresh a fish will smell of the salty sea, even after it has been thoroughly washed."

Firm touch

"When a fish comes out of the sea it's strong and packed full of energy so should feel hard. The longer it stays out of the sea, the softer it gets. So you can generally tell how old a fish is simply by how it feels."

Skin shine

"Hold the fish up to the light and see if the skin has an iridescent shine along its side. If it does, then it's fresh."

Sushi test

"Nearly every fish can be eaten raw. So the simplest test is to ask yourself whether you'd eat the fish raw as sushi. If the answer's no, don't buy it."