Mr Hannan, who has long campaigned for the NHS to be dismantled and replaced with a system of 'personal health accounts' once described the service as a '60-year mistake'.

Earlier in the week he used a speech in Washington to claim that the service was a 'Marxist system' and warned Americans to 'ponder our example and tremble'.

Insisting he sees the NHS as one of our great national institutions, Mr Cameron accused Mr Hannan of being eccentric.

He added: 'No one should be in any doubt, for the Conservative Party, the NHS is our number one priority.'

The NHS has its faults but its definitely better than nothing at all