The isolation of St Helena in the mid-Atlantic, one of Britain's few remaining colonies, is about to end: the Department for International Development is going ahead, at the second attempt, with the building of an airport to connect the island with the rest of the world.

One of three South African consortia that have pre-qualified for the contract will build the airport. So far, so good. With a population of only 4,000, St Helena has no viable economy beyond the remittances of its people working elsewhere, especially in the Falklands.

But many islanders have doubts about the move: with the airport development comes a new threat to the island in the shape of Aids, from which St Helena is currently entirely free. The labourers working on the project are expected to come mainly from South Africa, which has one of the highest rates of HIV/Aids infection rates in the world, and islanders are insisting that the workforce, of up to 300 men, should be screened for the infection.

In a letter to their governor and councillors, the Department for International Development has ruled against them. The letter states that South African law does not allow discrimination against HIV/Aids sufferers, and screening "cannot be justified on public health grounds as a means of reducing risk of transmission" and "is potentially a violation of human rights".

Of course, South Africa is entirely justified in a policy of non-discrimination within its borders, but St Helena is not South Africa. It seems to the islanders that the British government, which is responsible for their welfare, has an obligation to protect them in (as one of them puts it) their present "happy state of affairs".

Time is short. A process of consultation is being rushed through, with councillors' "surgeries" being held at two days' notice. A decision could be taken almost immediately.

An islander writes to me: "Most of us simply cannot understand it ... The official view is that Aids will come anyway, and testing is against human rights. What about the human rights of a population in a very unique situation? Isn't this akin to wiping out the South American Indian tribes?"

St Helena is hardly top of the news agenda, and hasn't been since Napoleon died there. It has survived wars, invasions, U-boat attacks and the ruin of its flax-based economy, but today its people feel threatened as never before. Will the government help them? Will parliament? And can we not raise our voices on their behalf?