The Office for Budget Responsibility said that spending on the state pension, social care and healthcare will rise from 14 per cent of Britain’s GDP to almost a fifth.

The report found that allowing more than 140,000 immigrants into Britain a year, equivalent to 6million people, would help increase the overall number of people who are in work and improve public finances.

Its analysis suggests that Britain’s borrowing as a propotion of GDP would rise to 99 per cent if there is a steady flow of immigrants. If there was a complete ban on immigrants, borrowing would rise to 174 per cent of GDP.

David Cameron has pledged to reduce the levels of immigration into Britain to “tens of thousands” during this Parliament. Last year the number of immigrants dropped by 89,000 to 153,000.

The report says: “Our analysis shows that overall migration has a positive impact on the sustainability of the public finances over our 50 year horizon.

Read further