Speaking on the Andrew Marr show on Sunday, the prime minister said Brexit could cause a “black hole” in public finances and threaten the “triple lock” guaranteeing state pension increases, the BBC reports.

The so-called ‘triple lock’ is a guarantee that state pensions will rise every year by at least 2.5% – or the rate of inflation or growth in earnings if it is higher – until 2020. It formed part of the Conservative’s 2015 election manifesto.

Cameron said: “Our pensions promise is based on a growing and succeeding economy.

“All the experts… agree that if we leave the single market, if we cut ourselves off from the most important market, our economy would be smaller and that has consequences.

“We would be taking a risk with growth, with jobs and with pensions. We shouldn’t do that – it is the wrong choice.”