In the grimy dockland suburb of Alcantara, Lisbon, a heavy, grey frosted-glass door in an equally forbidding office block currently offers an entrance to what has become the new El Dorado for a growing sector of the Portuguese workforce: Angola.

For centuries, the former colony was as ruthlessly exploited by its European masters as any other in Africa. But today, with the Portuguese economy floundering, the boot is firmly on the other foot. For most of the past decade, Angola's diamond-mining and oil-rich economy has grown by 10 per cent a year. With 7,000 Portuguese businesses already established there and clear linguistic, human and political links, too, when Angola started looking for a huge range of skilled workers from abroad to help rebuild the country, the old "mother nation" stood head and shoulders above the rest.

But for the recession-struck Portuguese to make it out there, there is only one legal path: head to Alcantara and that grim-looking door, behind which the Angolan consulate is currently processing Portuguese immigration papers at an average of more than 20,000 a year.

"It's for one reason: in Portugal, the recession is here to stay, and that's true for everybody," says Ricardo Bordalo, a Portuguese journalist from the Lusa news agency. Based in Angola between 2008 and 2011, he watched the number of his compatriots there increase from 20,000 to 130,000. "In Angola, after the war, the country was completely destroyed, and they needed people there. And many thousands of Portuguese had already lived there before independence. There's always been a special relationship between Portugal and Angola. Sometimes we hate each other, sometimes we love each other, and now it's our turn to go there. But it's not easy to get a visa: they make us suffer a little bit."

The Angolans themselves have no comment to make about the boom in immigration from their former colonial masters – at least not to this publication. "The Independent on Sunday is a very bad newspaper," one extremely well-built official said by way of explanation, albeit with a large grin, before firmly inviting me to turn around, leave the embassy building at once and "go and interview those Portuguese people over there".

Uniformly in their thirties and forties, the two dozen or so men and women milling about one Wednesday lunchtime almost all confirm they are – hopefully – Angola bound. However, they shy away from interviews and refuse point-blank to give their names. ("They wouldn't want to risk getting into trouble with the Angolan authorities," Bordalo points out.) Only one man, an electrical engineer – on condition of anonymity – is willing to go on tape.

"A lot of us want to go, just look at the queues," he says. "Many of my colleagues have already gone. It's impossible to find work here, even for highly qualified people. My wife has a master's degree in psychology, but her association was forced to close, and she is unemployed. What work there is pays very poorly. People like her are now earning €600 [£500] a month. Many graduates are working in call centres, selling stuff. Not that they sell anything."

It is true that Portuguese emigration is a well-established tradition – to the point where Portuguese economists estimate that, in the 1960s, money that was sent home from abroad contributed around a quarter of Portugal's GDP. However, destinations that were more popular in the past, such as the UK or other EU countries, are now far less appealing.

"All over Europe, there are millions of unemployed. Britain and France are not well [sic]. The same goes for the United States. There are many rich, but many poor," the electrical engineer points out. "In Angola, the economy is booming. It's not easy to get a visa, but I was contacted directly by the company there, and that makes it much faster. I'm going there for at least a year, and then we will see. Five or six years would be the target."

While unskilled people can get jobs there, the demand for unskilled labour is more limited – and woe betide anybody caught trying to enter Angola without the correct paperwork. "I heard of a bunch of guys who went there on tourist visas who then tried to start work on a building," the electrical engineer says with a chuckle. "They got put on the next TAP [the Portuguese national airline] flight back to Lisbon."

There is no attempt by Portugal's government to stop this brain drain, which has already seen an estimated 10 per cent of the country's workforce emigrate. Indeed, last December, the Prime Minister, Pedro Passos Coelho, suggested to teachers who were "supplementary to our requirements" that they "try Angola or Brazil, where there's a huge demand for primary and secondary school educators. We have a drop in population, and either they can retrain in other areas, or if they want to stay as teachers, look through the entire Portuguese-speaking market."

However, on arriving in Luanda, Angola may not appear to be as shiny an El Dorado as it seems from rainy, economically battered Portugal, where GDP is forecast to shrink by 3 per cent in 2012. "Some people go there and they get depressed in less than a week because they can't stand the streets full of rubbish, the fear of going out at night, the three-hour traffic jams and the corruption that exists in some areas," commented Antonio Fernandes – a Portuguese businessman returning to live in Angola last December as an emigrant – to the Spanish El País newspaper last year. "This is no country for softies."

However, at the moment, that heavy grey door fronting Angola's consulate in Alcantara is one of the fast-dwindling alternatives Portugal's beleaguered workforce can still take – hoping for some kind of viable future.

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Spain: The economic crisis is forcing 1,200 young Spaniards to emigrate to Argentina each month, Prime Minister Mariano Rajoy claimed last year. Around 30,000 Spaniards moved to Argentina between June 2009 and November 2010. Some 6,400 went to Chile and 6,800 headed for Uruguay.

Italy: The Italian economy has been at a virtual standstill since 2000 and around 600,000, often highly educated young Italians, have gone abroad in the past decade. Most have emigrated to North and South America. Many blamed Silvio Berlusconi for their country's rising unemployment rates.