Down the maze-like cobbled streets of Lisbon’s Alfama district – a once impoverished neighbourhood that’s now thriving – you might be surprised as fragments of conversation drift past. English, French, German – there’s even the rogue American drawl.

Because here, between the ancient houses that rise from the Tejo Estuary to the majestic Castele de Sao Jorge, you’ll find a community of young people from all around the world who’ve settled in the Portuguese capital and made it their home. The Alfama district is at the centre of Lisbon’s new cultural shift; but not everybody is happy about it.

Up-and-coming: Alfama has attracted many different nationalities (Getty/iStock) (iStock)

Lisbon’s been the European city break par excellence for some time now; the new Barcelona, if you will. It’s easy to see why: it enjoys a subtropical climate (the average temperature in December is a sultry 14C), the cost of living is cheap (you can rent a one-bedroom apartment in a central location for around €800 a month), it’s blessed with a vibrant bar and restaurant scene, and it provides easy access to the beaches of the Algarve.

But young, affluent millennials aren’t just holidaying in the City of Seven Hills. They’re moving here, and they’re doing it en masse. It’s all down to the way we work nowadays. Gone are the stable 9-5 jobs of yore; welcome to the gig economy.

According to one recent report, 60 per cent of 18 to 35-year-olds are actively looking to move abroad. Today’s workers are self-employed and geographically flexible; they’re freelancers who can work anywhere, provided the broadband is fast enough. So why live in a city like London – where rent is eye-wateringly expensive and the weather uniformly grey – when you could halve your living costs and wake up every morning to sunny skies?

“My girlfriend and I moved to Lisbon for a change of scene in 2013,” explains 31-year-old James Cave, who now lives in the up-and-coming Alcantara neighbourhood. “We had just started freelancing, and Lisbon seemed a great place to base ourselves. It was affordable and had great weather.”

Other newcomers to the city come once and love it so much they never leave. “I originally came here for a week for work, because I was producing music for Lisbon Fashion Week,” says Chris Savor, 31, who moved to the city three months ago and lives in the Principe Real district in the city centre. “I loved the vibe of the place so much I decided to live here!” Now, Savor spends €800 (£700) a month on rent – half of what he paid in the UK. “I love it here,” he enthuses. “The weather is always great, I love the old architecture and cobbled streets, amazing beaches and live music on the streets.”

Sail away: Lisbon provides quick access to the beaches of the Algarve (Getty/iStock) (Getty Images/iStockphoto)

But the pace at which people are moving to the city has quickened exponentially in recent years. “In around 2014, Lisbon started winning awards and getting listed as a place to visit. Suddenly, it seemed like everyone was going there,” says Cave. “The expat scene is a lot bigger than a few years ago.” He explains that younger expats tend to stay closer to the city centre and spend their weekends surfing or drinking in the bars of Graca, Cais do Sodre, Bairro Alto and Principe Real.

“My favourite thing about Lisbon is the overall quality of life I have here,” raves 37-year-old Kev Harrison, who lives in the Paco De Arcos area on the outskirts of the city. “It’s incomparable to anywhere else I’ve lived. The availability of fresh food at reasonable prices; the weather conditions; the cost and high standard of public transport – it’s all so much better.”

“My quality of life is great,” agrees Aristote Koen, 25, who recently moved to the Sao Domingo de Benfica area. “I rent a cosy room with weekly cleaning in a flat-share, for €370 a month. The city is multicultural, the food is great, prices are low and locals are friendly. You can also feel the historical and cultural wealth of the city, and there’s entrepreneurs from all over Europe, which is great.”

Local living: younger expats tend to hang out in the city centre (Getty) (Getty Images)

In particular, there’s a burgeoning nomad community in the city, comprised of freelance workers from all over the world who base themselves in the capital for months or even years at a time. Rosanna Lopes, 33, has been running a meet-up group for freelance workers for two years now. “My goal was to integrate the local startup scene with the digital nomad scene,” she says. Now her nomad community numbers around 150, has taken on a co-working space, and hosts regular networking events.

But not everyone is as delighted with Lisbon’s rapid pace of change. Lisbon residents’ associations have met to discuss what can be done to protect the interests of locals. Already rent is becoming prohibitively high for native-born city dwellers, and increasingly scarce.

“It’s becoming really expensive to find a long-term rental in central Lisbon,” says Agustin Cocola-Gant, an expert in gentrification and tourism at the University of Lisbon. “At the same time, demand has grown a lot, as European professionals, locals and international students move to the city. This is terrible for prices.”

And small private landlords are increasingly turning to rental services like Airbnb to make a living, decimating entire neighbourhoods, like the Alfama district. Grant tells me that on one street in Alfama alone there are 230 Airbnb rentals.

Inevitably, this has a corrosive effect on the fabric of Lisbon’s society. “In the last two or three years, locals have begun to complain,” he says. “The facilities and the services they use are disappearing. Traditional stores and bars that would have been cheap meeting places for locals are disappearing and being replaced with expensive cafes for English-speaking foreign students.”

Despite these concerns, Lisbon looks set to continue its relentless progress. And the city authorities are doing much to encourage this change – regulation is loose and taxes on short-term rentals remain low, as the city tries to stimulate the tourism industry to help tackle the still-high unemployment rates.