UP to half a million refugees and their relatives could move to Britain after 2020 in a "secondary flow of refugees" because of EU rules on the free movement of people, a major new report claimed today.

While Germany, Greece and Italy had borne the brunt of Europe's refugee crisis, those granted asylum could settle in the UK in the coming years once they had acquired EU citizenship, said Migration Watch UK.

The warning came after 18 Albanians, including two children and a woman, had to be rescued when their inflatable boat sank off Dymchurch in Kent on Saturday night, which lies just over 20 miles from France.

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Two British men were yesterday remanded in custody by local magistrates after being charged with immigration offences.

Migration Watch, which campaigns for tighter border controls, said an analysis of EU figures showed hundreds of thousands of people could take this route into the UK.

Lord Green of Deddington, chairman of Migration Watch UK, said: "The UK could well face a significant secondary flow of refugees from Europe in the coming years adding to the already huge strain being placed on housing and public services.

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"While the UK has so far been largely shielded from the crisis in southern Europe, this potential flow can only add to the impact of migration which is already seriously affecting communities across the country."

The report, entitled The Refugee and Migrant Crisis in the EU, says that according to Eurostat a projected 968,000 migrants will have been granted asylum or humanitarian protection for 2015 and the first quarter of 2016.

According to leaked estimates from the German authorities, each person granted asylum is likely to be followed by between four and eight family members.

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Migration Watch UK said that taking the lower figure of four would suggest the total inflow to Europe could amount to 4.8 million over a period of years; without taking account of any future arrivals who might successfully claim asylum.

The report calculated that if only 10 per cent of these refugees decided to move to Britain once they received EU citizenship, which can be claimed after around five years, then 480,000 people could arrive in the UK in the years following 2020.

Former Conservative Party leader and pro-Brexit campaigner Iain Duncan Smith said: “This report brings yet more evidence of the uncontrollable scale of immigration to this country.”

But the Stronger In campaign branded the report "completely false and bogus" and said its numbers were "completely wrong".

It also questioned Migration Watch UK's independence, accusing the organisation of having "close links with Leave campaigners".

Emma Reynolds, the pro-EU Labour MP for Wolverhampton North East, said: "The evidence shows the overwhelming majority of refugees will never get the right to come to Britain. There is only one thing we know for certain; leaving Europe will wreck our economy.”

Meantime, a top union official warned that Britain's coastline was facing one of its biggest ever breaches of its borders as an unprecedented number of small boats and dinghies smuggled in migrants.

Lucy Moreton, general secretary of the Immigration Services Union, said large stretches of Britain's coastline were being left unpoliced and officials simply did not know how many people had sneaked into the country undetected.

In an earlier development, Lord West, the former head of the Royal Navy, claimed Britain was at risk from terrorists and traffickers because of the lack of boats that patrolled UK waters.

“It is a complete mess. We are taking a calculated risk with our own territorial waters,” he declared.

Elsewhere, Nigel Farage insisted Albanian migrants arriving in Britain had to be returned to France.

"It is essential that a clear message is sent that no migrant arriving on our shores by boat is allowed leave to remain", said the Ukip leader.

"The spectacle of boats crossing the channel must be avoided. If we do not make it absolutely clear, we are likely to find the English Channel becoming a mortuary as economic migrants take to its unpredictable waters in unseaworthy vessels,” he stressed, adding: "We must not make the same mistake as the EU has done over the Mediterranean situation."

Meanwhile, Robert Stilwell, 33, from Dartford, and Mark Stribling, 35, from Farningham, appeared at Medway Magistrates Court accused of people smuggling.

Mr Stilwell and Mr Stribling were charged with conspiring to facilitate the entry of non-EU nationals, and remanded in custody to appear before Maidstone Crown Court on 27 June.