Britain is going backwards.

We have all got so used to life expectancy ticking steadily ever upwards that many of us had started taking that progress for granted, yet a new report by the legendary epidemiologist and former government adviser Sir Michael Marmot provides a timely bucket of cold water. For women living in the poorest parts of Britain, lives are now getting shorter; both men and women are also spending longer in chronic ill health towards the end of their lives, meaning the time they do have left is painfully constrained. The gears are crunching into reverse, according to his findings for the independent charity the Health Foundation.

Here, then, is the really big litmus test of this government’s commitment to its new electoral coalition, because the crude political reality is that it will often be Boris Johnson’s new voters dying before their time. People in the so-called “red wall” seats captured by the Tories at the last election can expect to live for only 60.9 years in good health compared with 65 years for those in Tory-held seats and 61.4 years in the places where Labour clung on. Marmot can find no biological explanation for life expectancy falling – it’s not as if humans have just naturally hit a ceiling on how long we can live – and is explicit about identifying austerity, and the everyday hardship that followed, as the likely culprit. But he is also clear that simply declaring austerity to be over isn’t enough to reverse the tide. If there’s money to spend now, it needs to be spent on things that are not historically Tory priorities.

Many Tory MPs simply haven’t grasped the full implications of the promises their leader has been making

So far Johnson’s government has been undeniably good at connecting culturally with ex-Labour voters who felt their party no longer understood them. These newfound red Tories are finally getting not just the Brexit they craved but the curbs on immigration and tough talk on terrorism or crime many of them wanted, while Labour is mired in battles over trans rights or Jeremy Corbyn’s lingering influence which can only push them further away. But that’s the easy bit, because socially conservative voters and traditional Tories have always met in the middle on these issues. The next step is the painful one because it means rewiring the way a Conservative administration naturally thinks and spends.

Talk of levelling up the country is cheap but actually raising health outcomes in the deprived north up towards those of the south is a slow, unglamorous and expensive business that involves swallowing difficult truths about the relationship between poverty and sickness. It means accepting that people will inevitably struggle to make healthy choices when they’re reliant on tins from the food bank or run ragged from working three jobs – arguments that a certain kind of Tory tends to dismiss as excuses for failing to take personal responsibility – and reshaping welfare policy accordingly. It means ploughing money into cheap, stable and decent socially rented homes as well as helping first-time buyers priced out of London. It means a national strategy to reduce health inequalities, something Tony Blair’s government introduced and David Cameron’s quietly dropped. And it means hard choices between what the Tories’ more affluent traditional base in the south wants, versus what their new base in the north was promised at the election.

The howls of pain greeting any suggested means of raising cash in next month’s budget – from raids on pension tax relief to scrapping the freeze on petrol duty – suggest many Tory MPs simply haven’t grasped the full implications of the promises their leader has been making. If they really mean what they say about reversing decades of decline in the north, then it’s going to cost, and no Conservative should need to be told that money doesn’t grow on trees. And if they didn’t really mean it, then every report like this one brings them one step closer to being found out.

• Gaby Hinsliff is a Guardian columnist