By Evan Davis
It was about two years ago. I was returning from a weekend trip to France and found myself in a long queue of traffic on a dual carriageway just outside the port of Calais.
There right in front of us were dozens of young men walking between the vehicles and opening the backs of trucks to clamber inside.
They were evidently mostly Afghans, taking advantage of the fact the traffic was moving slowly to try anything to sneak a ride into the UK.
All this less than 30 miles from Kent.
For me, any thoughts of disapproval at the unruly behaviour I was witnessing evaporated at the sight of a teenage boy cowering dangerously at the top of a lorry driver's cab under the back canopy.
He was not a trouble-maker. He was obviously petrified but still so desperate to get on to a car ferry to Britain, he was going to take the risk.
I felt like stopping the car to ask him why. What journey had he taken to get here and where did he think it might end? What is so good about our country that people would go to such lengths?
It was largely the vivid memory of that scene which made me eager to be involved in Panorama's examination of the economic migrants who risk everything to try and reach Britain illegally.
It is a chance to tell the migration story from the point of view of those trying to get into our country, rather than those of us lucky enough to be here already.
Journalist Shoaib Sharifi followed the journey from Kabul where he met fellow Afghans as they set out to reach the EU in Greece.
And in Africa, fellow journalist Kassim Kayira began in Lagos in Nigeria and travelled up through Africa to Morocco, a route taken by many African migrants fleeing poverty.
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Evan Davis presents Panorama: Breaking into Britain
The perspective from the UK and European border agencies on how they address the growing numbers desperate to reach the EU was my remit.
In Kabul, Shoaib met Fakhrudin, a father of seven who had decided to sent his eldest son to Europe, relying on the illegal people smugglers to help 18-year-old Sear reach Britain. Such is the demand to get out that it is one of Afghanistan's few growth industries.
"I'm doing this only so that my son can have a better life," Fakhrudin said, adding that he knew he was putting his son in harm's way for the gamble of that better life.
There are no guarantees of success and the price - just to get as far as Greece - is £4,700. For an extra £2,600, the smugglers tell Afghans they will get them as far as France. A further £700 will get you to London, they are told.
For those who do make it across the border with Iran and on to Turkey, the last stage before reaching Greece is the Evros river.
Perhaps the saddest revelation was the indecency of the reception in the European Union.
It is in Greece that many Afghan migrants' illusions of Europe as a welcoming place are quickly shattered.
Many have run out of money and find themselves sleeping rough on the streets of Athens with no hope of moving on to western Europe.
One young couple, Abdullah and Zarminah, made the trip with their three young children. They spend hours walking the children around the local squares to tire them out so that they will fall asleep on the pavement behind shrubs. They sleep in shifts in order to be able to watch over the children.
African migrants pay smugglers to help them risk their lives to cross the Sahara
"The children ask me, is this really Europe? Is this Europe where we have no place to sleep?" said Zarminah, who relies on a local charity to feed the children once a day.
Kassim Kayira meets migrants stranded along the route from Nigeria to the Mediterranean who have also run out of money to move on from Agadez in Niger.
They tell of being extorted at every turn, by passport control at borders and police along the way to people smugglers demanding thousands to take them on the dangerous lorry trip across the Sahara desert to Morocco. The former route via Libya has been abandoned amid that country's civil war.
For the women who have risked everything, the dangers are ever more grave. They described to Kassim the smugglers who demand sex in exchange for their passage, even if they have already paid for their trip. Many make it no further than the brothels of Africa.
Kassim said: "I was thinking, this could be my sister, this is someone's mother, you know, this is someone's daughter. Their parents are waiting. If they call back home, what are they going to tell their parents?"
Unfortunately what Shoaib, Kassim and I learn is that those scenes I witnessed in Calais two years ago are just a slice of the greater problem.
Shoaib Sharifi met penniless Afghans sleeping rough on the streets of Athens
The risks the migrants take and the suffering they endure on their journeys are only matched by the resourcefulness they exhibit to travel thousands of miles unaided and their determination to succeed that is reinforced with every failed attempt.
All for what? Most of the journeys are futile.
Economic migrants are too often trapped without money or documents, unable to get into their destination of choice in Western Europe and penniless to turn around, give up and go home.
I defy anyone to watch the programme and not think that Greece and Italy badly need help in dealing with undocumented arrivals - a situation made even worse by the flood of arrivals fleeing violence in north Africa.
At the heart of this investigation lies a simple dilemma - to tolerate the suffering on our own continent is unconscionable - but to alleviate the suffering by simply opening the door might attract vastly more people than we can realistically cope with humanely.
We meanwhile are trying to maintain complete mobility across borders for the population of the rich world while trying to build ever higher walls to deny that mobility to the world's poor.
I am sorry to say our examination of the issues does not deliver a solution.
Perhaps there is not one to be had.
Panorama: Breaking into Britain, BBC One, Thursday, 16 June at 2100BST and then available in the UK on the