Wes Streeting has defended Labour’s plans to use the private sector to help cut the NHS care backlog, arguing that a failure to do so would result in a “betrayal” of working-class people who cannot afford to pay for care.

The shadow health secretary said his approach was a “pragmatic but principled one” as he doubled down on his remarks this week about “middle-class lefties” whom he said risked putting ideological purity ahead of patient care.

In an interview with the Guardian, however, he insisted the NHS would be privatised “over my dead body”, adding that his longer-term ambition was for nobody to be forced to pay and for the NHS not to rely on private care at all.

Streeting has aroused suspicion among some Labour MPs, health unions and NHS campaigners for his embrace of private healthcare as a way of cutting the backlog, which stands at 7.6m treatments in England alone.

But he said that he was “fed up” with the binary view that ignored the fact that after 14 years of Tory rule there was now a two-tier system that meant some people could afford to go private to be seen faster, while those who could not were left behind.

“From a leftwing perspective, it’s not right that people who are poorer are priced out of faster healthcare,” he said. “It goes against everything I believe in as a Labour politician. As somebody who might lead a middle-class life now, but with working-class roots, it’s a betrayal of the people I grew up with.”

He said that a Labour government would use the private sector for “as long as it takes” to get people seen faster, blaming the Tories’ failure to invest sufficiently in staff, technology and capacity.

“In the longer term it’s my ambition to make the NHS so good that no one feels forced to go private, and to make sure the NHS has the capacity it needs so that it doesn’t need to pay for people to go private either,” he said.

But he repeated his criticism of the left of his party. “I will never allow ideological hobby horses to come at the expense of patient care,” he said.

“The argument I’ll make unapologetically is that those people who say we shouldn’t use the private sector to cut waiting lists will have to be honest about the fact that they’re telling people who can’t afford to go private that their leftwing principles say they should be waiting longer.

“They can’t use the usual get out of jail free card of saying ‘we want investment in the NHS’. Of course we all want investment in the NHS, a Labour government will deliver investment in the NHS, but it takes time to build that NHS capacity back, and people have to be honest about that.”

Streeting has repeatedly underlined how his priority as health secretary would be to reform the NHS. But he said: “The lesson of the last Labour government is that it’s investment plus reform that delivers results … We did it before and we’ll do it again.”

He said a Labour government’s economic inheritance would make investment difficult – but said that the shadow chancellor, Rachel Reeves, had consistently prioritised the NHS when it came to spending priorities.

Streeting said that he was “not indifferent” to arguments that sending people private could cost the NHS more but suggested that his hands were tied by the lack of capacity in the service.

He argued that there should always be a door open to working with the private life sciences and medical tech sectors. “If we can combine our country’s leading scientific and tech minds with the care and capacity of the NHS then the sky is the limit,” he said. “I’m fed up with this binary view.”

Streeting defended his criticism of “middle-class lefties” in the Sun newspaper this week, saying he was up for having the argument about how Labour needed a pragmatic approach to the NHS to guarantee its survival.

“I was taking on my critics who are accusing me of privatising the NHS and they do tend to be middle-class lefties. I say this as someone from a working-class background who is now a middle-class lefty.

“I don’t think it’s a disparaging term. These are the people who are most outraged by what I’m saying. I am taking on the argument and ultimately I want to win it. I don’t think people should be offended by what I’ve said.

“My argument is both a principled and pragmatic argument for not just saving the NHS, but for making sure that it continues to be there for us as a public service free at the point of use.”

He insisted that Labour continued to be a party of progressive values, despite some criticism from the left over its stance on issues including Gaza and the climate crisis, which has led some core voters to shift away from the party.

“For the Labour party it has always been a moral crusade to make our country a more fair, equal and just society, but we’re not a debating society, we’ve got to be a party of government that’s able to influence and effect change.

“I don’t think people on the left should take for granted a Labour victory at the general election – we’ve seen too many false dawns before … If you’re serious about taking the country forward it does mean building a broader consensus and sometimes some compromise.

“I don’t think that’s a dirty word in a country that has been riven with divisions by the most rightwing Conservative party in modern history.”