Lisbon springs into life for the colourful San Antonio celebration: A personal pilchard trail

Fiona Dunlop prepares for the fado-full festivities with a plate of Portugal's famous sardines

Alfama decked out for the San Antonio 'festa' (Jose Frade)

I am sitting at a table in a cobbled Lisbon backstreet, shaded from the scorching sun by laundry flapping from balconies above. Laid out on the checked tablecloth is a bowl of succulent razor clams, a basket of crusty bread, a huge green salad, a fast emptying bottle of vinho verde and, the pièce de résistance, a plate heaped with glistening, grilled sardines.

Bruno and Ricardo, my Lisbon insiders from We Hate Tourism Tours, are giving me a lesson in how to eat these tasty morsels, in advance of the mega-feast to celebrate the San Antonio Festival this coming weekend, the Portuguese capital's big summer kick-off. "If my grandfather saw you eating them with a knife…!" cries Bruno. So I follow their example, laying the sardine on a "plate" of bread, carefully peeling back the skin, then removing and devouring each delectable fillet.

San Antonio, the patron saint of Lisbon and of sweethearts, was born in Alfama, an alluring district of ice-cream-coloured façades that spills down the hill from the castle to the Tagus river. Snaking alleyways, tiles and staircases abound, as do bars, churches and fado music. On the night of 12 June, the entire community surfaces to follow 40 costumed performers competing with parades from the city's 16 other quarters in a boisterous carnival atmosphere.

Festooned with paper garlands and fairy lights, Alfama, once the main fishermen's quarter, also reeks with fishy aromas from dozens of street barbecues set up for the long night of partying. Though bleary-eyed, Lisboetas continue the festa the following day, while young couples celebrate the much sought-after San Antonio mass wedding in the eponymous church – paid for by the city council.

Although sardines have long been considered a delicacy in Japan, in southern Europe the pungent, oily fish have tended to sit on the bottom rung of piscine delights. Not in Portugal, though, where they are eaten both fresh and tinned (the country has a long tradition of preserving fish by salting, with canning in olive oil dating back to the mid-19th century).

But just as the gourmet world twigged their appeal, sardine supply is suffering. "Sometimes you can't find them or the prices are astronomical," says Bruno, "so a lot come from Morocco." In fact, that morning at the fishermen's market in Costa de Caparica, there were none left. Luckily, we found our joy at the central Caparica market, along with those equally appealing razor clams.

Nevertheless, Lisbon is Sardine Central. Specialist shops are packed with exquisitely packaged tins, there are sardine T-shirts, key-rings, chocolate sardines in replica tins, ceramic sardines, recipe books, beach towels and even an annual competition for fishy graphic designs awarding five winners €2,000 each.

Fishermen at Cacilhas (Fiona Dunlop)

My personal pilchard trail continues on Lisbon's grandest square, the elegant, arcaded Praça do Comércio, the hub of 18th-century Baixa that embraces the river to symbolise Portugal's long relationship with the sea. At Can the Can, a restaurant name that hardly needs explanation, a huge chandelier made of pristine tins illuminates shelves of conserves. At an outside table, I tuck into a tasting plate where sardines wrapped in a grilled courgette or forming a textural combo with red pepper on toast slip down nicely. Afterwards, I stroll over to a fishing-boat recycled as an open-air, landlubbers' bar to sink into a deck-chair and toast the majestic Tagus. Yet again, Lisbon knows how to welcome the summer.

Next day I am back on the river, this time aboard a ferry-boat that, in 10 minutes, chugs across from Cais do Sodré to Cacilhas, a former port renowned for its towering statue of Christ (in which a lift spirits you skywards for spectacular views) and winding main street of seafood restaurants. Of course I spot grilled sardines sizzling temptingly outside a charming old place called Cabrita, then lust after a shellfish cataplana a few doors away at Solar Beirão. But the river beckons, so I end up practising my new dissecting skills at a chrome yellow table by the water's edge. This is Ponto Final, a 15-minute walk from the ferry terminal past derelict warehouses where local anglers share wide-angle views of Lisbon.

A selection of ultra-fresh seafood at the Mercado da Ribeira (Fiona Dunlop)

Gradually, my seafood horizons are expanding, so back in the Cais do Sodré district I zip across the road to inspect the 1930s Mercado da Ribeira, reinvigorated a couple of years ago as an upmarket food hall. Here, a line-up of design-conscious stands serve anything from sushi to ceviche to risotto, in contrast to the traditional fresh food market next door. Although the slick design is impressive, it is not what I have come here for, nor do many locals seem enamoured.

That evening it's the turn of the jellyfish – not on my plate but gliding mesmerisingly through cerulean water in a huge tank beside my table. I am at Largo, a glamorous restaurant in Chiado carved out of a vaulted monastery, with a priest still in residence above ("I hope he blesses us," whispers the attentive chef, Miguel Castro e Silva). Here I indulge in delicate sashimi-style starters and sole with scallop, trumped by a tender octopus tentacle bedded in chickpea purée. Blessed indeed.

Yet this is topped by my gargantuan last supper in the riverside district of Belém where, in a modernised cervejaria (brasserie) heaving with chattering Portuguese families, I plough through a succession of garlicky clams, primeval-looking goose barnacles, succulent Algarve prawns and a dressed lobster fresh from the tank. Not a pilchard in sight, but when my marine degustação finally ends at the airport, I am overjoyed to discover shops brimming with dazzlingly designed tins of my faithful friends. Adeus sardinhas, I'll never forget you.

Getting there

TAP Portugal (0345 601 0932; flytap.com) flies to Lisbon from Heathrow, Gatwick and Manchester from £121 return. Ryanair (0871 246 0000; ryanair.com), easyJet (0330 365 5000; easyjet.com) and BA (0844 493 0787; ba.com) all offer flights to Lisbon.

Visiting there

We Hate Tourism Tours (00 351 913 776598; wehatetourismtours.com) offers tours such as Lunch in our Street for €30.

Eating there

Can the Can (00 351 914 007 100; canthecanlisboa.com); Cabrita (00 351 21 275 1780). Solar Beirão (00 351 21 276 6019; solarbeirao.pt). Ponto Final (00 351 21 276 0743). Largo (00 351 21 347 7225; largo.pt).

Staying there

Hotel Britania (00 351 21 315 5016; hotel-britania.com) has 32 rooms from €160, B&B.

More information

Fiona Dunlop was a guest of Turismo de Lisboa (visitlisboa.com)