Johnson has denied that the future of the NHS would be at risk under his government.
In a 1995 column unearthed by Business Insider, Boris Johnson called for patients to be charged to use the National Health Service, with free care maintained only for "those who are genuinely sick, and for the elderly."
The UK prime minister called for the extension of charges for services including ambulance journeys to prevent free healthcare being "abused" by those who can afford it.
"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 magazine.
"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 for one of his children, who then turned out not to be seriously ill, 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."
Johnson said that the only reason charges hadn't been introduced by the Conservative 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 wrote.
"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."
Footage uncovered this week by the blog Red Roar showed Johnson, in a 2002 speech to the House of Commons, calling for a breakup of the "monopolistic" NHS.
"I think it's all very well to treat the NHS as a religion, but it's legitimate for some of us to point out that, insofar as it is a religion, it is letting down its adherents very, very badly," he said.
The Labour Party said the column proved that Johnson was secretly planning to dismantle the NHS.
"This is yet another quote direct from the horse's mouth showing Boris Johnson does not support a free at the point of use NHS," the shadow health secretary, Jonathan Ashworth, told Business Insider.
"These revelations are coming thick and fast and demonstrate Johnson's extremist views on the NHS.
"More cuts, privatisation and now charges are on the way if Boris Johnson and his Conservative Party get five more years."
The Conservative Party did not immediately respond to a request for comment.
The future of Britain's healthcare system has become a central issue in the upcoming general election, with Johnson's opponents accusing the prime minister of planning to include the NHS in a post-Brexit trade deal with the United States.
The prime minister has denied any intention to include the NHS in trade talks.
However, leaked minutes of meetings between US and UK officials obtained by the Labour leader, Jeremy Corbyn, suggested that US officials were keen to include the issue in talks.
Corbyn said they showed that the US's negotiating objectives included full access to the UK markets for US healthcare companies.
President Donald Trump on Tuesday denied any such plans, telling reporters in London that he wanted "nothing to do with" the NHS.
"If you handed it to us on a silver platter, we'd want nothing to do with it," the president said.