Whatever David Cameron and his fellow European leaders tell us, the enormous one-way flow of migrants to the West is changing Europe irretrievably and for ever.

Twelve thousand migrants have been rescued from people-smugglers' boats off the coast of Libya and heading for Italy in the past week alone. And more – maybe a million more – who come from the Middle East, Africa and South Asia will soon be on their way there, too.

For more than 15 years now, I have reported on the steady flow of migrants heading for Europe. In countries across the Continent, I have spoken to those who have travelled thousands of miles, and never ceased to be amazed by their resilience and determination to find a better life.

More than a thousand refugees of sub-Saharan origin arrived in Salerno from the Channel of Sicily carried by the Siem Pilot ship

In recent days the EU Navy made several rescues of boats from Africa including people with scabies

Shocking pictures earlier this week showed the the vessel, crammed with refugees, starting to lean on to its side before refugees start diving into the water as it capsizes

I have witnessed fatal tragedies as migrants make their way across perilous seas, despair and disappointment as their hopes turn to ashes, and resentment and anger from Europeans who feel their own countries and cultures are threatened by this relentless tide of incomers.

But this week, on the quayside of pretty Porto Empedocle in Sicily, I came across a scene that convinced me more than ever that the explosion in migration is completely out of control.

I watched as 540 Syrians, Libyans and Moroccans came ashore from the Italian naval ship that had plucked them from the sea after the boat taking them to a new life across the Mediterranean capsized.

Coming down the gangplank they waved at the waiting crowd of TV crews, international charity workers, UN officials, police and Red Cross doctors, as if they were celebrities on the red carpet at the Cannes Film Festival. The crowds cheered back, shouting 'buongiorno' (good morning) and clapping as the arrivals set foot on dry land.

Such was the surreal carnival atmosphere that it was almost impossible to comprehend that hours earlier these smiling migrants had been involved in a life-or-death struggle. Or that they were in Italy only because they had paid smugglers, now growing rich in chaotic Libya, for a place on a flimsy wooden boat to illegally enter Europe where they were now being accepted with open arms.

Crammed to the hilt, their boat sank after 240 of the passengers had already been taken off and ferried to safety on the Italian navy ship.

The arrivals, including tens of pregnant women and at least 107 children, many clutching teddy bears, then lined up to fill in registration forms and have their photographs taken by immigration officers

At least five migrants drowned off the Libyan coast on Wednesday after the heavily overcrowded boat they were sailing on overturned, the Italian navy has revealed

The remaining 300 passengers had then panicked and rushed to one side of the vessel, tipping it over. Only the best efforts of the navy, who threw scores of red lifebelts and rafts into the water, saved all but a handful of them.

The ship's captain, Francesco Lavezzo, took his turn in front of the cameras in Porto Empedocle. He said an uplifting memory for him was when a rescued migrant girl smiled with excitement as she was given a white teddy bear by his crew on board the ship.

It was a tear-jerking story – and one that sugars and distorts the tragic but ugly truth about this sorry episode.

For whether we like it or not, large numbers of those coming ashore in Sicily were not refugees fleeing persecution or war. Many were economic migrants, who may have come from countries run by despots, or live on less in a year than most in the West get paid in a week – but who have now slipped into Europe illegally with few questions asked.

The port-side party atmosphere also seemed offensively incongruous. For next to the noisy quayside welcoming party stood a line of hearses waiting to take five bodies to a Sicilian morgue. They were the migrants who had drowned after the boat upturned – the ones who had not been so lucky.

The hearses would be in use again shortly afterwards. A second boat full of migrants capsized the following day and up to 30 were feared drowned as another 88 were hoisted to safety.

But it's not just Sicily. Across the water on Italy's mainland, the southern port of Salerno yesterday received more than 1,000 migrants from sub-Saharan Africa who had been recovered by a Norwegian ship.

As soon the Siem Pilot docked, those most unwell were taken on stretchers to makeshift medical tents set up on the quay. Among them, 173 were found to have scabies.

The arrivals, including tens of pregnant women and at least 107 children, many clutching teddy bears, then lined up to fill in registration forms and have their photographs taken by immigration officers.

Twelve thousand migrants have been rescued from people-smugglers' boats off the coast of Libya and heading for Italy in the past week alone

Officials said they came from 20 countries, mostly sub-Saharan, including Nigeria, Mali, Cameroon, Somalia, Gambia, and Senegal. They had departed from the Libyan city of Sabratha on Tuesday night in dinghies.

What seems incontrovertible about the biggest migration crisis in Europe since the Second World War is the extraordinary number of people who are prepared to risk their own lives, and even their children's, to reach the West.

Yes, the risks are huge, but they understand that the odds of survival are stacked in their favour, and greedy people-traffickers in Libya encourage them by telling them so. And there is also an official safety net: under EU rules, member countries have a duty to send their navy to rescue anyone in peril on a vessel in their own territorial waters.

These rescue vessels simply act as a magnet for more migrants to try the crossing. They know that if they reach Italian waters, they will most likely survive and be taken to their destination even if the smugglers' craft in which they are sailing does not make it.

What is certain is that some of those brought to safety in Porto Empedocle this week will have vanished from Italy within weeks. They will simply walk out of the migrant hostels after taking a hot meal and a shower.

The Norwegian ship 'Siem Pilot Stavanger' arrives at Manfredi pier of Salerno port carrying 1,017 refugees

Last year, a staggering 47 per cent of the 153,000 migrants who arrived in the country did not even attempt to claim asylum. Many ran away, travelling to northern Europe to try their luck at getting into prosperous Britain, Germany or Sweden. Of course, some do stay in Italy. In the midst of economic woes, the country has been forced rapidly to extend its hospitality.

Last year the highest number of migrant housing places Italy had to provide was 67,000. This March that had risen to 106,000.

An increasing number of them are unaccompanied children less than 18 years old. They have been sent as forward scouts by their families back home, who one day hope to join them.

Each migrant, whether a grandmother, a young man looking for work or a baby, is an extra mouth to feed, another human to clothe who needs a bed to sleep on. No wonder Italy is buckling under the strain.

The EU foreign policy chief Federica Mogherini estimates that half a million more migrants are currently waiting in Libya hoping to reach Europe on traffickers' rickety boats. Migration experts have said the true number could be twice that figure.

Officials said they came from 20 countries, mostly sub-Saharan, including Nigeria, Mali, Cameroon, Somalia, Gambia, and Senegal. They had departed from the Libyan city of Sabratha on Tuesday night in dinghies

For other paths to Nirvana are closing. Migrant numbers on the route from Turkey to Greece, through the Balkans and up to northern Europe have dwindled in the face of border checks and barbed wire fences in less welcoming Austria and Hungary.

More than a million people reached Europe that way last year after Germany's Chancellor Angela Merkel invited in all Syrian refugees fleeing civil war and the horrors of the Islamic State which has taken over swathes of their country.

What a can of worms she opened. What a seismic shift she has caused in Europe. For countless numbers of those who took up her offer were not refugees from beleaguered Syria at all.

Thousands upon thousands chanced their luck by pretending to be Syrians, while in fact they hailed from the Balkans, from Albania, Pakistan, Afghanistan, Morocco, Egypt, Iran, Iraq or from Africa.

Today, safely in Germany, many don't even bother to lie about their background and no sanctions are imposed on them for their deception.

Last year I did actually meet a Syrian in Calais, a well-dressed man who had booked in to my hotel there. The 32-year-old was a civil servant who had reached Europe by sailing from Turkey to mainland Greece on a traffickers' boat.

Once there he headed north to France by train.

'I am going to Britain,' he told me with certainty at the French port. 'I have the cell phone number of an agent here in Calais who I will pay to hide me inside a car on a ferry to Dover.

Thousands upon thousands chanced their luck by pretending to be Syrians, while in fact they hailed from the Balkans, from Albania, Pakistan, Afghanistan, Morocco, Egypt, Iran, Iraq or from Africa

'I am not going to wait with these other migrants in the mud of the camps. They are not Syrians. They are from Africa and Afghanistan where there is no big war like ours.'

When you look at the latest asylum claims in the UK, you realise what he said is right. The figures have jumped by more than a third to the highest annual level for more than a decade, according to the Office for National Statistics.

In the year to March, the largest numbers came from Iran, followed by Eritrea, Iraq, the Sudan, and Pakistan – all countries which certainly have their troubles but nothing like the difficulties facing Syria. Indeed, Syria accounted for only 2,500 of the total 34,687 UK applications.

Libya's former dictator Colonel Gaddafi, before he was deposed and killed in 2011, promised the West that he would turn Europe into a Muslim country if the EU did not support his power struggle with insurgents and extreme Islamists.

He threatened to allow traffickers to operate unhindered – they already existed on a limited scale in Libya – and let them flood our Continent.

Last month, Frontex, the EU Border Force, warned that terrorists are infiltrating Europe by pretending to be refugees. It pointed out that two of the bombers in last November's Paris attacks arrived on a smugglers' boat from Turkey.

At the G7 summit in Japan this week, David Cameron warned that Islamic State is gaining a foothold in Libya, and pledged Britain would send a Royal Navy warship to patrol Libya's coast to help tackle people-smugglers.

But he failed to acknowledge that it was his own gung-ho decision to help remove Gaddafi using British armed forces that reduced Libya to the terrifying anarchy it is in today.

Frankly, the Prime Minister's gunboat diplomacy smacks of gesture politics. The plan is for the vessel to turn back smugglers' boats – but there are simply too many of them.