Boris Johnson has claimed he "vastly underestimated" how much the UK would save by leaving the EU, saying it will be much more than the £350m a week he claimed as part of the Vote Leave campaign.

The Foreign Secretary has told The Guardian that the country's contribution to the EU budget was already at £362m a week and would rise to £438m by 2021, the last year of an expected transition period.

Johnson has been repeatedly slammed for the controversial claim, with critics arguing that it does not take into account the rebate or other benefits received from EU membership. He has also received criticism for implying it would be automatically redeployed into the NHS.

But the minister doubled down on his claims, telling the paper:“There was an error on the side of the bus. We grossly underestimated the sum over which we would be able to take back control.”

And he insisted the cash can and should be used to bail out our struggling public health system, saying: “As and when the cash becomes available – and it won’t until we leave – the NHS should be at the very top of the list."

His latest comments have been seized on by his political opponents.

Labour MP and Open Britain supporter Alison McGovern said: “Our NHS is in the middle of a winter crisis and Boris Johnson’s solution is to return to the scene of his previous crimes and promise ever larger slices of pie in the sky.

“Boris’s Cabinet cheerleading for leaving the Single Market and the Customs Union will lead to less money - not more - for public services like our NHS.

"Boris Johnson promised £350m a week for the NHS while telling us the EU could go whistle but then backed a £40bn divorce bill. Does anyone think he’ll leave our NHS doing anything other than whistling in the wind for the extra resources it badly needs?"