The UK could need up to ten million immigrants by 2025 to avoid a pensions meltdown, according to a new report.
The warning comes from the Cass Business School, which warns that a major rethink of the UK's economic model will be needed in the coming years.
As well as a sharp increase in immigration, Britons are likely to have to work longer and save more for their own retirement.
Professor Lee Mayhew of Cass Business School said: "The UK is facing some tough decisions in terms of state pensions provision.
"We can increase our work force via migration, we can work longer or we can increase contribution payments - even if we do this it only keeps the current state pension system stable until 2030."
Last month the Turner Report warned that the shortfall in pensions would require a combination of higher taxes and longer working lives.
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