On the wall of Jonathan Ashworth’s office is a whiteboard itemising the woes of the National Health Service: the four million patients on waiting lists, the continually missed A&E targets, the 80,000 operations cancelled in 2017. As the 70th anniversary of the NHS’s creation approaches (5 July), Ashworth believes the service is in its worst state for two decades. “It’s not a winter crisis, it’s an all-year-round crisis,” the shadow health secretary told me when we met in parliament.

Although the Conservatives have formally protected health spending since 2010, the NHS has still endured the longest period of austerity since its foundation. Historically, expenditure has risen by an average annual rate of 4 per cent, but it rose by just 0.84 per cent in the last parliament (and will rise little more in this one).

Ashworth has pledged that Labour would commit an extra £45bn to health and social care over the next five years. But he conceded that “even on our spending plans, towards the end of the parliament, we know there would still be huge demands on the NHS, which is why we do need a debate and discussion on how we fund it”.

Labour’s 2017 manifesto vowed to increase spending by raising taxes on corporations and the top 5 per cent of earners (those on salaries of more than £80,000). But Ashworth suggested that a more ambitious settlement was needed.

“Under the previous Labour government, Gordon Brown laid out a case for the long-term investment needs of the National Health Service and then increased National Insurance and hypothecated the yield from that to the NHS. That was actually a popular tax rise.” (A 2002 ICM poll found that 76 per cent of voters backed the policy.)

Conservative MPs such as Sarah Wollaston, the chair of the health select committee, former minister Nick Boles and backbencher Johnny Mercer have recently supported a dedicated NHS tax. “It’s an interesting debate and it’s a debate that we should engage in,” Ashworth told me. “The country needs to have a discussion about the future financing of the NHS for the 2020s and the 2030s.”

As we spoke, Ashworth brandished a copy of In Place of Fear, the 1952 book written by Labour’s Nye Bevan, the NHS’s founding father. “I want to be the health secretary who returns the NHS to its Bevanite origins,” said Ashworth, who is planning a series of speeches and campaigns to mark the 70th anniversary.

“Bevan talked about the NHS as being a great civilising moment for the nation … It was about an assault on health inequalities in society. And throughout the last 70 years, we have still not resolved this issue of health inequality. Today, a child born in Chelsea is still likely to live on average nine years longer than a child born in an inner-city constituency like mine [Leicester South].”

Ashworth, 39, grew up in a working-class family in Salford, Manchester. His mother was a barmaid and his father a croupier. His ties to Labour, which he joined as a 15-year-old, are deep and long-standing. He became national secretary of Labour Students in 2000 and was for many years an aide to Gordon Brown (including as deputy political secretary at No 10). Ashworth’s wife, Emilie Oldknow, is an executive director of Labour (responsible for governance, membership and party services).

For years after his 2011 election to parliament, Ashworth struggled to avoid being typecast as a backroom fixer (he served as deputy chair of the party and on Labour’s ruling National Executive Committee). But as shadow health secretary since October 2016, he has found his voice.

In February 2017, Ashworth spoke movingly in a parliamentary debate of growing up with an alcoholic father. “From the age of eight or so, going to my Dad’s meant I was effectively the carer,” he recalled. “It was very typical for my Dad to pick me up from school and literally fall over because he was so drunk.” The then Conservative public health minister, Nicola Blackwood, was moved to tears by Ashworth’s words, and she spoke in support of him.

“I was inundated by people who got in touch to say that they grew up in similar circumstances,” he told me. “I’ve come to realise that addiction services in this country have been neglected and ignored and not given the political priority they should. And it’s another reason why we need to invest in the public sector because the private sector provision is just woeful.”

In view of the government’s troubles, I asked Ashworth whether he was concerned by Labour’s slight or non-existent opinion-poll lead over the Conservatives. “I’ve always said that we have to be persuading people,” he said, adapting the words of the Canadian prime minister Justin Trudeau: “Conservative voters are not our enemies, they’re our neighbours, they’re our friends and we need to be convincing them.”

Though Ashworth does not hail from Labour’s Corbynite left (he backed Yvette Cooper as leader in 2015), he is valued by the leader’s office as one of the shadow cabinet’s most reliable performers.

“Nah, there’s plenty of Labour MPs who fancy their chances of being the next leader,” Ashworth said when asked if he was interested in leading his party one day. “I don’t need to be bobbing around in that pool as well.” (Exactly the answer that an aspirant leader should give.) “I want to be the health secretary… The message will go out loud and clear on day one that things are changing in the NHS.”