Image copyright Getty Images Image caption The UN warns about migrants not using their skills, leaving "surgeons flipping burgers"

Migration remains one of the most potent international political dividing lines - with arguments about controlling borders and pressures on local services.

But a report from the United Nations warns that once migrants have arrived, host countries often fail to make use of their talents.

The UN has published an analysis showing only 30% of migrants with degrees are in graduate-level jobs.

It comes ahead of a UN convention this year that aims to make it easier for migrants to use their skills and work experience in their new countries.

"Stories of immigrant doctors who are cab drivers or surgeons who are flipping burgers bring to light how much potential is being wasted the world over," said Ita Sheehy, an education adviser with the UN High Commission for Refugees (UNHCR).

As well as being frustrating for ambitious migrants, the UN says, it's wasteful for economies to have high-skilled people in low-skilled jobs.

Evidence of skills

The analysis, jointly produced by the UNHCR, Unesco's global education monitoring report and the Education Above All charity, says that the biggest barrier can often be the lack of international recognition for qualifications.

Even though someone might have advanced professional qualifications in their home country, if there is no system of mutual recognition, they are effectively treated as if those skills did not exist.

Image copyright Getty Images Image caption Migrants rescued from the Mediterranean being brought ashore in Spain

About three-quarters of migrants are in countries without an agreement on recognising qualifications from the countries that they have left.

"Some migrants and refugees find the procedures for getting their qualifications recognised so complex that they cannot find work at all," said Ms Sheehy.

This is a global problem, affecting people displaced by conflict across the Middle East, Asia and in Africa, as well as those arriving in Western Europe and North America.

It's particularly bad for refugees or those escaping violence, who might arrive with little documentation or evidence of qualifications.

"When fleeing a conflict, packing a diploma is likely not to be top of your mind," said Manos Antoninis, director of Unesco's global education monitoring report.

Lack of recognition

It's also an issue for mobile professional workers, who might study and train in one country but then later move to live and work elsewhere.

In 2019, the UN plans to introduce a "global convention on the recognition of higher education qualifications", intended to make it easier for people to show the value of their qualifications if they move to another country.

Image copyright Getty Images Image caption Migrants can find themselves working in jobs below their skill levels

It promises "fair, transparent and non-discriminatory" approaches to help people get their qualifications assessed by education authorities in another country.

But at present it's very much a patchwork quilt of national regulations - and even when there are agreements in place, this can be more in theory than in practice.

An international agreement from more than 20 years ago promised a framework for recognising qualifications - but the UN report says that most of the signatories have never put it in place.

The United States is highlighted as a place where skilled migrants are particularly likely to be stuck in low-paid jobs.

And in South East Asia, a reciprocal arrangement meant to recognise professional qualifications has rarely been used, says the report.

But it commends efforts in Germany and Norway to recognise the qualifications and work skills of those arriving.

Unable to use skills

Even in jobs where there are staff shortages, it can sometimes be difficult for migrants to use their expertise.

Image copyright Getty Images Image caption Migration remains a political divide: President Trump considers designs for a border wall with Mexico

In England, there has been a prolonged teacher recruitment problem.

But Beata Pawlak, a secondary school teacher from Poland, says she found it difficult to find work as a teacher or teaching assistant when she moved to live in London.

She has a postgraduate degree and English-language qualifications and 16 years of teaching experience in Poland but has struggled to get into teaching in London.

Instead, she became a nanny and said many other fellow professionals had ended up in jobs such as cleaning or in other non-graduate work.

"I know the work is below my skill level but in the end decided it wasn't worth the effort of applying again and again for teaching work. It was humiliating," she said.

More from Global education

The editor of Global education is Sean Coughlan (sean.coughlan@bbc.co.uk).