David Cameron was today accused of giving up on tackling immigration, as it emerged the government's hopes of balancing the books depend on an extra 1.1million migrants arriving over five years.

Chancellor George Osborne plans to eliminate the deficit and achieve a surplus of more than £10billion by 2019-20.

But the official economic watchdog says this can only be met thanks to high levels of net migration every year, well above the 'tens of thousands' target which David Cameron has promised before two elections.

Former Home Office adviser Nick Timothy said rising levels of net migration were proof that the ministers had given up trying to control the numbers of people coming to Britain.

According to data from the Office for National Statistics, net migration in 2014-15 will be 330,000, falling to 256,000 next year and 232,000 in 2016-17

George Osborne will only meet his target to get Britain's finances back in the black if the Tories break their promise to cut immigration

Official forecasts for migration are used by the Office for Budget Responsibility to predict how many will be in work and adding to the economy each year.

According to data from the Office for National Statistics, net migration in 2014-15 will be 330,000, falling to 256,000 next year and 232,000 in 2016-17. Over five years the total comes to 1.1million.

Even from 2020 onwards the figure is expected to be more than 185,000, well above the level targeted by the government.

A predicted 1.1million rise in the number of people in work is almost entirely the result of rising immigration.

Nick Timothy, pictured, said the rising levels of net immigration is proof that the government has abandoned all hope of controlling numbers

The OBR said in documents published at the time of last week's Autumn Statement: 'The participation rate is expected to rise modestly over the next three years – in part due to net inward migration that is focused among people of working age – and then to fall back to its current level as the population ages.

The Government is no longer trying to cut net migration – and we can expect the numbers to keep going up and up Ex-Home Officer aide Nick Timothy

'The 1.1 million rise in employment over the forecast period can therefore be explained entirely by additional population growth, which has been marginally revised up in light of the ONS’s latest projections.'

Mr Timothy, who worked for Home Secretary Theresa May until earlier this year, said rising levels of net migration were proof that the ministers had given up trying to control the numbers of people coming to Britain.

'The trouble is, as the Autumn Statement made plain last week, other than in the Home Office the Government is no longer trying to cut net migration – and we can expect the numbers to keep going up and up,' he wrote on ConservativeHome.

Mr Timothy added: 'There is a new reason why the Treasury is keener than ever on mass immigration.

'It might not bring any significant economic benefits for existing British citizens, but it does mean a bigger population, and a bigger population means a bigger economy overall, which means that the effect of spending cuts increases when the deficit is measured as a percentage of GDP.'

The Office for Budget Responsibility produces data on the impact of various factors - including rising productivity, people working longer hours and a larger population. It shows how rising numbers of migrants in work (shown in pink) will be an increasingly important driver of economic growth

The Chancellor plans to eliminate the deficit and achieve a surplus of more than £10billion by 2019-20

HOW DAVID CAMERON'S 'TENS OF THOUSANDS' PLEDGE UNRAVELLED 'We would like to see net immigration in the tens of thousands rather than the hundreds of thousands.' David Cameron, Jan 2010 'Levels of immigration can return to where they were in the 1980s and 90s. Net migration to this country will be in the order of tens of thousands each year. No ifs. No buts. That's a promise we made to the British people.' David Cameron, April 2011 'When we made that comment ... we were very clear that was what we wanted to do. It remains the objective towards which the Prime Minister and others are working.' Theresa May, Nov 2014 'I think we will keep the target. It is important because it is about not just dealing with those coming into the system but also about making sure that those people who shouldn't live here actually leave.' Theresa May, March 2015 'Our action has not been enough to cut annual net migration to the tens of thousands. That ambition remains the right one.' Conservative party manifesto, April 2015 Advertisement

New figures released last week show that net migration hit a record high in the year to June at 336,000, higher than the ONS forecast for the year to March 2916.

Researchers said the latest rise was down to a 'statistically significant' increase in the numbers of people arriving in the UK, with immigration at 636,000 - up 62,000 on the same period last year.

The surge is driven in part by a major jump in the number of Bulgarians and Romanians coming to the UK, up 61 per cent in a year.

Mr Cameron has repeatedly refused to 'cave in' on his promise to cut net migration to the tens of thousands, despite the figure leaping to its highest annual total records dating back four decades.

Net migration - the difference between new arrivals and those leaving - is up a third to 336,000 in the year to June.

It comes after the number of people settling in the UK leapt by 62,000 to 636,000 while the number who left in 12 months dropped by 20,000 to 300,000.

Mr Cameron has promised his planned changes on benefits for migrants would limit the numbers coming from the EU.

Latest figures show that net migration of EU citizens increased by 42,000 to 180,000 in a year.

Last week Foreign Secretary Philip Hammond warned Britain could vote to leave the European Union over fears of an 'uncontrollable wave of migration'.

He said the public mood had shifted in the wake of the migrant crisis spreading across Europe.

In a speech in Rome, he added: Since the migration crisis began earlier this summer, the poll numbers have changed and the most recent poll published yesterday showed that by a small margin a majority are now in favour of leaving the EU.

'I am pretty clear from talking to my own constituents this reflects the effect of the migration crisis and fear of the future and fear that Europe is losing control of the situation.'

Mr Cameron has demanded curbs on benefits for migrants, include a ban until their have been in the UK for four years - something other EU leaders are resisting.

But Mr Hammond said: 'That is non-negotiable if we want to get agreement that Britain's future is in the European Union.'

Campaigners Migrationwatch said there was no figure in the OBR report that details the net contribution of migrants to public finances. The group said that, in general terms the OBR assumes migrants are likely to be of working age, but that this was a ‘very simplistic assumption’.

Labour said: ‘This is a Tory government which is failing on its own measures. From the economy to immigration they are breaking their own promises.’