Mass immigration from outside Europe is ‘unlikely to fall significantly’ unless ministers introduce tough new measures, a report warns today.

The scope to tackle migration from non-EU nationals will be limited unless the Government takes ‘further and determined action’, according to a respected think-tank.

MigrationWatch said net migration from outside the Brussels bloc - those people arriving minus those leaving – was likely to run at 155,000 a year until 2021.

Mass immigration from outside Europe is ‘unlikely to fall significantly’ unless ministers introduce tough new measures, a report warns today

That would be the equivalent of more than the population of Slough – 146,000 – arriving from the rest of the world every 12 months for the next five years. It currently stands at 175,000 in the .

Until Britain finally quits the EU, controversial freedom of movement rules mean it is a requirement to let in the European citizens.

However, the Home Office does have the power to control the numbers coming from the rest of the world.

Measures to do this have included closing loopholes on student visas and raising the minumum income threshold for non-EU workers.

Lord Green of Deddington, chairman of MigrationWatch, said: ‘Migration Watch UK has a remarkable record in estimating future migration'

But an analysis by MigrationWatch, which campaigns for controlled borders, predicted that between 2016 and 2021 net migration from non-EU citizens would average 155,000 annually. The report was published ahead of a new set of official migration statistics being published tomorrow THURS.

It based the findings on a series of major studies carried out by the Home Office of work, study and family visas issued between 2004 and 2010.

Researchers calculated how many recipients were still in the UK with permission to remain or had settled.

From this, they worked out that an estimated an average 85,000 of the 415,000 non-EU citizens handed visas each year from 2011 to 2016 would be in the UK after five years.

On top of this, MigrationWatch predicted 35,000 a year would overstay their visas and adjustments to official statistics would also add another 35,000 migrants a year – making a total of 155,000 a year.

At the same time, workers are also expected to pour in from EU nations fleeing stagnant eurozone economies with spiralling unemployment. Net migration from the EU was 133,000 last year.

Lord Green of Deddington, chairman of MigrationWatch, said: ‘Migration Watch UK has a remarkable record in estimating future migration.

Until Britain finally quits the EU, controversial freedom of movement rules mean it is a requirement to let in the European citizens

‘We now say that, unless determined action is taken, it is extremely unlikely that non-EU migration will fall significantly in the next five years.

‘This should be a wake-up call for the government to take further action if overall net migration - after subtracting British emigration - is to be brought down to sustainable levels. Brexit should help considerably but further action on non-EU migration is essential.’

The continued influx has left egg on the face of the Government which made it a manifesto pledge to reduce numbers to the ‘tens of thousands’.

Failure to control the country’s porous borders was the spur for millions of people to vote for Brexit.

Soaring immigration has been blamed for contributing to dampened down wages in some low-skilled industries, such as agriculture and food processing, and kept British people out of jobs. It also heaped pressure on public services, including schools and healthcare, say critics.

Prime Minister Theresa May has restated the vow to cut net immigration to below 100,000 – but warned it could take more than four years.