Labour must be bolder and deliver real change, Wes Streeting has said in his first Commons speech since resigning as health secretary, saying that he quit the government because it was “currently losing” the fight against populist nationalism.

Streeting reiterated his view that leaving the EU had been a damaging mistake for the UK, and argued that young people had been let down by a system stacked against them.

Streeting resigned last week and called on Keir Starmer to quit as prime minister. It had been expected he would launch a formal leadership challenge, but he seemingly failed to get the necessary support from 80-plus Labour MPs.

In his contribution to the king’s speech debate, Streeting had no direct criticism of Starmer, and praised him for keeping the UK out of the US-Israel war against Iran.

But he was very critical of the government’s wider approach, saying it had been too cautious and had allowed parties such as Reform UK to hijack the idea of patriotism.

“Never waste a minute – that’s been my mantra in government, and it’s why I don’t believe our party has time to waste in government treading water,” he told MPs. “The Labour party was elected to deliver real change. We still can.”

In a long section taking aim not just at Reform but also at the SNP in Scotland and Plaid Cymru in Wales, Streeting said Starmer’s government had failed to take the battle properly to nationalists.

“I left the government because we are in the fight of our lives against nationalism, and it is a fight that we are currently losing,” he said. “Unless we change course, we risk handing the keys of No 10 to Reform, and I do not want that on our consciences.

“For the first time in our history, nationalists are in power in every corner of the United Kingdom. Scottish and Welsh nationalism represents an existential threat to the future integrity of the United Kingdom, and Reform UK represent a threat to the values and ideals that have made this country great.”

He went on: “For too long and for too often, patriotism in Britain has been left to the loudest voices and the narrowest arguments, as though love of country belongs to one tribe, one party, or one point of view. But the Britain I believe in is bigger than that, because patriotism is not about who you exclude, it is about who you stand beside.”

Streeting added: “The nurse from Nigeria is not the enemy of the factory worker in Newcastle. The family fleeing war is not responsible for the cost of living crisis. Division is the oldest trick in politics, and Britain deserves better than that.”

In a speech on Saturday, Streeting said he would like to rejoin the EU. Speaking in the Commons, he said that in his maiden speech in 2015, he had “argued that none of the problems facing our country would be solved by leaving the European Union”.

He went on: “Today, in the dangerous and volatile world we find ourselves in, dominated by an unpredictable superpower in the USA, a rising superpower in China, and a failed superpower in Russia, it is even more clear that we would have been better off leading Europe than leaving the European Union, not despite our sovereignty and the need to control our borders, but to enable those things.”

Streeting also set out what he said was a breakdown in the inter-generational contract, which had left young people bearing the biggest burden from Covid but then unable to afford a home and at risk of being pushed out of the jobs market by AI.

He said: “Patriotism isn’t a lecture the old deliver to the young. It’s a relationship, and for generations, Britain understood that relationship as a social contract. You work hard, you play by the rules, you contribute to society, and in return you can build a decent life, a secure job, home of your own, a family if you want one, and the hope and conviction that your children will do better than you did.

“So, the question isn’t whether young people would fight for their country but when their country is going to fight for them. This is our generational challenge.”