In a 1995 column unearthed by Business Insider, Boris Johnson said patients should be charged for using the National Health Service.
"If NHS services continue to be free in this way, they will continue to be abused, like any free service," he wrote in the Spectator.
"If people have to pay for them, they will value them more."
He added that those who say that "in the future the NHS should be for those who are genuinely sick, and for the elderly" were "bang on the nail".
Writing about his experience of calling for an ambulance, Johnson asked, "Why should I not be charged, say, £50 for that inglorious episode, a fraction of its real cost?"
Johnson added that "it seems reasonable that the middle classes should be required to stump up for non-essential services they can well afford."
The PM said the only reason charges hadn't been introduced by the Tory government at the time was political "cowardice".
"I will not be charged for the ambulance because politicians dare not take away from the middle classes the benefits they have accrued under the welfare state," he continued.
"For the same reason they will not take away all the other instruments of universal provision such as child benefit, disability allowance, and the rest. It is greed on our part, and cowardice on theirs."