His voice is low and deep and his eyes are closed as he sings of his homeland.

The beat of the four ravannes - African drums - is infectious. Jean Redi Bancoult's arm is raised and he points to the middle distance.

His thoughts are not here, in this dusty backyard amid makeshift buildings in Cassis - one of the poorer neighbourhoods of Port Louis, the Mauritian capital.

His thoughts are 1,200 miles away, on a group of small islands in the Indian Ocean - a place young Jean has never seen.

He sings in Creole. He sings of the islands of Peros Banhos and Salomon, part of the Chagos archipelago, which was leased to the US to allow for the development of the huge Diego Garcia military base.

The song speaks of long nights drinking the local brew, baka, and dancing the sega. A certain rhythm has come from Chagos, it says.

Refugee Adeline Jaffor with her family outside their shack

There is a certain rhythm for the Ilois - the islanders - as they call themselves, but for 30 years now the rhythm, more often than not, is one of despair.

For all this time the Ilois have been banned from their homeland, expelled in an act of late colonial arrogance breathtaking in its execution.

Not settled well

The sad history of the Chagos islands is what brought me to Mauritius, and the knowledge that this mostly forgotten story is being exhumed in the High Court of London this week, as the islanders bring a unique legal case against the British Government, to fight for the right to return to their homeland.

The Ilois have not settled well in Mauritius. That much is plain to see. Now numbering about 5,000 people, they are scattered in slums around Port Louis.

Their young people - those born in Mauritius - are discriminated against. They find it hard to get work. Their parents and grandparents, those born in the Chagos islands, are like fish out of water.

They are uneducated, they have not adapted to metropolitan life. They spend their days dreaming of their paradise lost.

The young singer Jean's uncle, Olivier Bancoult, is the man bringing the court case.

The British administrator breaks the news to the islanders

Inside his tiny house, he stands in front of a Nelson Mandela poster, and smiles - his inspiration, he says.

Olivier was four when he was first brought to Mauritius on what his family thought was a temporary break.

I remember my mother crying, he tells me, when we were told we could not go home.

'It is not fair'

He pauses, and then you see in his eyes the steel that has brought this poor electrician to take on the might of the British Government.

It still makes me very sad now, he says, the way my people have been uprooted is not fair.

This origins of this uprooting are mired in Cold War politics and superpower angst.

In 1965, when Mauritius was negotiating its independence from Britain, the then Prime Minister Harold Wilson made it clear there would be no deal without the Chagos islands being separated from Mauritius, and retained by Britain.

The islands were of great strategic significance - situated right in the middle of the Indian Ocean - they were in the heart of an area prized by the then Soviet Union and China.

What Mauritius did not know was that Britain had already done a deal with the United States - they would lease the largest island, Diego Garcia, for use as an air base and ship refuelling station.

But the Americans did not want a "population problem", as they put it.

There were about two thousand people living on the islands, mostly working in the coconut plantations. Descendants of African slaves and Indian plantation workers, the Chagos islanders had lived there for generations.

Seewoosankar Mandary, who used to work at the weather station

So Britain began a systematic, but highly secret, programme of resettlement.

No return

Families were accustomed to taking periodic trips to Mauritius by the only boat available.

Once there, they - like Oliviers' family - found a return passage was refused to them.

This policy continued for several years, until the programme was stepped up. The plantations were closed down, food supplies ended, and then in 1970, the people on Diego Garcia were called together and told they would have to leave.

Seewoosankar Mandary remembers that day well. He was working on the small weather station on the island, and took some photographs of the moment the people were told by the British administrator they were being evicted.

"He told the people there will be changes in the way the place is run. In a few weeks time you will not be able to stay. The military will come and you will have to go," Mr Mandary remembered.

All this was only revealed in 1975, through a United States congressional inquiry into the Diego Garcia military base.

But even then, the British government tried to cover it up. They claimed the Illois had no right to live on the islands, and said they were just temporary contract workers from Mauritius and the Seychelles.

In fact, declassified Foreign Office documents discovered at the Public Records Office in London reveal the policy of deception.

Embarrassment

One memo, dated 28 July 1965 says: "A small number of people were born there and, in some cases, their parents were born there too. The intention is, however, that none of them should be regarded as being permanent inhabitants of the islands."

The court case being heard in London this week is an undoubted embarrassment to the British Government, and they have just revealed they have begun a feasibility study into whether the Ilois could return to some of the Chagos Islands, despite the continued presence of the American base on Diego Garcia.

Unsupecting islanders were taken away in boats

A Foreign Office statement released to the BBC says: "The government wants to be as practical and positive as we can. We are taking the advice of consultants to assess whether people could return to the outer islands and what the environmental impact would be."

A generation later, and life has improved for most of the Ilois, but not by much.

I watched one lady, Adeline Jaffor, speak at a so-called grand assembly of the islanders as they organised their legal fight.

She spoke with eloquence and great passion about the plight of their people.

Afterwards she took me to her home and I began to see why. She showed me the broken corrugated iron walls and roof, the holes where the rain pours in.

She showed me the two beds where she and her ten children and grandchildren sleep.

Adeline is a widow, and she works a cleaner in the central market. "I'm really angry," she said, "Over there we had a good life, we lived together happily. But we have none of that here. I'm very very angry. I want to go home."