Portugal, struggling to comply with the terms of a €78bn financial rescue package, is encouraging oil-rich Angola to invest in its debt-stricken economy, highlighting a reversal of roles with few parallels among European countries and their former African colonies.

Pedro Passos Coelho, Portugal’s prime minister, said during a visit to Angola on Wednesday and Thursday that his centre-right government would look “very favourably” on Angolan investment in its €7bn privatisation programme and other areas.

His appeal for investment underlined the extent to which the relative positions of the old imperial power and its former colony have changed, as Portugal faces the deepest recession in Europe while Angola expects its economy to grow 12 per cent next year.

“A post-colonial role reversal on this scale is unprecedented,” said Paulo Gorjão, director of the Portuguese Institute of International Relations and Security. “The challenge is to make it mutually beneficial for both countries.”

Portuguese professionals, unable to find jobs at home, where unemployment will rise above 13 per cent next year, are emigrating to Angola in ever increasing numbers, reversing a migratory flow previously dominated by Angolans fleeing the country’s civil war, which ended in 2002.

According to Portugal’s emigration observatory, the number of Portuguese living in Angola, which gained independence in 1975, increased from 21,000 in 2003 to 91,900 last year. Meanwhile the number of Angolans living in Portugal fell by about 1,000 to 26,500 in 2009, as many Angolan and Brazilian emigrants return to their own thriving economies.

Angolan companies have become important shareholders in a number of high-profile Portuguese banks and utilities, providing a rare source of foreign investment amid the global downturn. Some Portuguese lenders have derived more than 40 per cent of their income from Angola as the domestic market contracts.

In June 2010, the value of Angolan investments in listed Portuguese companies was estimated at more than €2bn, close to 4 per cent of the total listed value.

Angola’s national oil company, Sonangol, is the biggest single shareholder in Millennium BCP, one of Portugal’s largest listed banks. Banco BIC of Angola, which is partly owned by Isabel dos Santos, the eldest daughter of José Eduardo dos Santos, Angola’s president since 1979, owns 10 per cent of Banco BPI, another big Portuguese lender.

Mr Passos Coelho told Angolan companies they were “very welcome” to invest in next year’s sale of state holdings in TAP-Air Portugal, the national airline, ANA-Aerportos de Portugal, the national airport operator, and public transport companies.

Mr Gorjão said one of Angola’s main ambitions was for Sonangol, seen by analysts as almost a proxy for an Angolan sovereign investment fund, to acquire a stake in Galp Energia, Portugal’s dominant oil and gas utility, in which the Portuguese state has a 7 per cent holding.

Mr Passos Coelho made it clear during his visit that the Lisbon government would not raise any objections, clearing the way for a deal.

However, according to some observers, efforts by international organisations, including the European Commission, to combat corruption could act as a constraint on Portugal’s economic ties with Angola, which has a poor record for business transparency and fighting corruption.

For an economic perspective, Mr Gorjão said Portugal should also be concerned not to become over dependent on Angolan investment. “Angolan companies already have important positions in some of the Portugal’s leading business decision centres,” he said. “The need to keep investment sources diversified should always be taken into consideration.”