Europe is in the grips of its biggest movement of people since the Second World War. European leaders tend to refer to the situation as a migrant crisis, rather than a refugee crisis. Legally, there is a crucial distinction. The UN refugee agency says it boils down to whether the person is being pushed or pulled: a migrant is someone who voluntarily moves to another country, and intends to live for at least a year there; a refugee is someone who flees persecution, conflict or war.

UN officials say a vast majority of the 137,000 people who crossed the Mediterranean into Europe in the first half of the year were refugees fleeing war, conflict or persecution in countries including Syria, Afghanistan and Eritrea.

British Prime Minister David Cameron talked about "a swarm of people coming across the Mediterranean seeking a better life, wanting to come to Britain because Britain has got jobs, it's got a growing economy, it's an incredible place to live". His choice of words was widely criticised by human rights advocates as offensive and misleading. Anna Musgrave, Advocacy Manager at Refugee Council, said: "It's incumbent on the Prime Minister to show leadership, to use responsible language, to remember we're a country with a proud tradition of protecting refugees and upholding human rights."

In this gallery, IBTimesUK looks at Britain's history of welcoming refugees, from the approximately 100,000 Jews who moved to Britain during the Second World War, to the tens of thousands of Asians who made their homes in Britain after they were expelled from Uganda by Idi Amin.

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October 1922: Refugees from the Turkish city of Smyrna (known today as Izmir) arrive safe in Plymouth. Up to 100,000 Greeks and Armenians were massacred in the Greco-Turkish WarGill/Topical Press Agency/ Getty Images
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May 1937: More than 4,000 Basque children arrive in Southampton, having been rescued from the horrors of the Spanish Civil WarE Dean/Topical Press Agency/Getty Images
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November 1938: Refugees who escaped Nazi Germany return from the fields at Flint Hall Farm, Hambledon, as they are trained to become farmersGeorge W Hales/Fox Photos/Getty Images
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December 1938: Some of the thousands of Jewish and non-Aryan German child refugees, known as the Kindertransport, arrive in England at HarwichFred Morley/Fox Photos/Getty Images
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November 1939: Refugees from the Nazi invasion of Czechoslovakis rehearse in the gardens of Farley Hall in Derbyshire, where they run their own theatreFox Photos/Getty Images
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March 1939: More German-Jewish refugee children arrive at Southampton on the US liner Manhattan as part of the Kindertransport programmeFox Photos/Getty Images
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August 1939: Polish refugees come ashore in Britain at the outbreak of World War TwoAllan/London Express/Getty Images
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May 1940: Refugees from Belgium arrive at a station in LondonJA Hampton/Topical Press Agency/Getty Images
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July 1940: A ship packed with a 'swarm' of refugees leaves for England from St Jean de Luz, the last 'open' port on the Atlantic Coast in FranceKeystone/Getty Images
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October 1945: Jewish refugee children, survivors of Belsen concentration camp, attend classes at Wintersmill House, Durley, in HampshireKeystone/Getty Images
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October 1950: Latvian refugees arrive in Penzance after escaping from a Baltic portFox Photos/Getty Images
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November 1956: The first of 2,500 Hungarian refugees offered settlement in Britain arrive at Blackbushe airport in HampshireTopical Press Agency/Getty Images
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April 1965: A young girl clutches her doll for comfort. She is one of a group of German refugee children who have come to England for a holiday with an English family. She wears a label round her neck which says 'Croydon'Philip Townsend/Express/Getty Images
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September 1971: Vietnamese war orphans travel on a coach on their way from London Airport (Heathrow) to the Pestalozzi Children's Village in SussexCentral Press/Getty Images
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September 1972: Ugandan Asians arrive at Stansted Airport on the first of several specially chartered flights to Britain shortly after Ugandan military dictator Idi Amin expelled all Asians from the country.Keystone/Getty Images
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October 1978: A group of Vietnamese boat people hold a large banner saying, "Our Gratitude to Elisabeth II and the English people for hospitality to the Vietnamese refugees"Colin Davey/Evening Standard/Getty Images
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April 1999: Ethnic Albanian refugees wave from the window of an aeroplane as they arrive at Leeds airportReuters
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April 1999: Wellwishers wait to greet some 160 Kosovar refugees as arrive at Leeds Bradford airportReuters
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August 2015: Syrian refugee Raghad al Sous poses for a portrait in Huddersfield. She braved bombings in Syria to keep studying at school before fleeing in 2013 to join her mother, who had been granted refugee status in Britain. She is now about to start studying at university with the hope of becoming a hospital pharmacist. Her plans for a well-paid career contrast with concerns among some Britons that migrants are a drag on the country's economy and public servicesAndrew Yates/Reuters

About 3,000 people live in makeshift encampments in Calais in northern France, with many trying each night to jump onto trucks or trains heading to Britain, or even walk to the UK through the 31-mile tunnel.

Britain is spending millions of pounds on improved fencing, CCTV and other security equipment to protect the tunnel.

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August 2015: Home Secretary Theresa May greets British security forces near the Eurotunnel entrance in Calais, as Britain announced it had invested €15m (£10.9m) in installing fences, surveillance cameras and infrared detectors along the tunnel, to prevent migrants and refugees from reaching the UKRegis Duvignau/Reuters

Britain gained almost 330,000 people through migration in the last year. It's the highest figure on record and a headache for the Conservative government amid a political storm about immigration.

Rising immigration has fuelled support for the UK Independence Party (Ukip) which wants to sever ties with the EU and impose much tighter entry rules. "These figures reflect Borderless Britain and total impotence of the British government," Nigel Farage said, calling for Cameron to negotiate tighter border controls with the EU.

Yet academic research points to a positive impact from immigration for developed economies. The Organisation for Economic Co-operation and Development estimates that migrants accounted for 70% of the increase in Europe's workforce in the 10 years to 2014. European employers say they need more foreign workers to fill a range of jobs from highly-skilled positions to lower-paid menial positions that native Europeans no longer want to take.

Researchers also say immigrants contribute more in taxes than they take in state benefits in the UK. A study by University College London found immigrants to Britain represented a net positive for the public accounts and brought with them qualifications that would have cost nearly £7bn pounds in education funding. Furthermore, immigrants were less likely to claim benefits than native Britons.