Unreported World's investigation into the latter-day exodus of Eritrean refugees towards Israel, to be broadcast this evening, makes for unsettling viewing. There are unmistakable biblical parallels - here is a persecuted population fleeing a nasty regime for what they feel to be the Promised Land. And in doing so they have to make their perilous way through the Sinai desert. But those who cannot pay the huge sums of money demanded by the people smugglers face kidnapping, torture and in some cases death.

Even if they succeed in reaching the border they could still be shot at and killed by Egyptian guards. And if they make it to the Israel side, they could be captured and returned by the Israelis to the Egyptians - and the Egyptians have a nasty habit of illegally sending them back to Eritrea where they face torture or worse.

So why are these poor, persecuted people trying to get to Israel in the first place? The picture painted of the country by the refugees, and by presenter Ramita Navai, is of a liberal, prosperous nation - one of the fastest growing economies in the world.

According to the programme, Israel has acted fairly towards the refugees. Those lucky enough to be arrested and not given back to the Egyptians as so-called "hot returns" are taken to detention centres where their cases are assessed - and many are allowed to stay and work legally.

However, even this best-case scenario does not usually offer a happy ending. Of the estimated 20,000 Eritreans now living in Israel, many are destitute and even those who work are forced to live in overcrowded conditions.

This documentary does not address the question which would be on the lips of most Israelis - that if a bunch of smugglers in pick-up trucks can breach the border with such ease, what could a determined terrorist achieve? Clearly, this is something which has exercised minds in the Israeli government - there are plans afoot to build electrified fences along the length of the frontier.

I hope this does not mean that Israel will be turning its back on these desperate people who are prepared to risk their lives to achieve something that most of us take for granted - safety and enough to eat.

One woman called Sion tells of how she was held hostage by her smugglers in the Sinai desert. She was given one piece of bread and one tomato to eat each day, and was allowed to use the toilet once a day. At all other times she was chained to four other hostages in an underground cell. She was only released when her family and friends managed to sell everything they possessed to raise a $12,000 ransom - a fortune in Eritrea.

Navai asks Sion if, knowing what she knows now, she would make the same dangerous journey again. She replies that her suffering in Eritrea was such that she would- willingly.

This is great TV, It is also almost impossible to watch.