It is now a month since the Conservatives romped to victory in the general election. Though the picture was complex, there was one movement of voters that was larger than many had anticipated. This was the levels of direct switching from Labour to the Conservatives by working-class voters across northern England and the Midlands.

“Labour leavers”, “traditional Labour voters” – we’ve heard many names for this group. But the most accurate description of their circumstances is one coined in the summer of 2016 by Theresa May. For these voters are the “just about managing”, those who “work around the clock”, for whom “sometimes life can be a struggle”. They feel a financial squeeze but are above the threshold to be eligible for social benefits.

Polling conducted by my company, JL Partners, immediately after the election showed that most defectors to the Conservatives were in this “C1/C2” group, in “unskilled” white-collar or “skilled” blue-collar jobs: they are the receptionists, the plumbers, the forklift drivers of Britain. And they are now key to the Conservatives’ continued electoral success.

Policies aimed at one can upset the other. An example is the national living wage. Focus groups that I ran during my time at No 10 showed that many in the 'just about managing' felt it was unfair

“Get Brexit done” and the toxicity of Jeremy Corbyn helped win them over in December. There were elements of domestic policy aimed at these voters in the Conservative manifesto, with higher spending on public services, and a cut to national insurance. But the Conservatives will need a more positive and longer-lasting domestic agenda, aimed fully at their concerns, to keep them on board.

But there is a challenge in catering so strongly to this group, which strikes at a tension at the heart of modern Conservatism. Helping them does not equate to helping the most vulnerable in society. This is because these new Tory voters are not the poorest – far from it. That same polling reveals that the average household income of voters who moved to the Conservatives is £29,000. They are voters who have one car belonging to their household rather than none at all. Two-thirds of them have been on a foreign holiday in the last three years. They feel they struggle with money, but the pressures mean cutting back on extras rather than not putting food on the table.

Successfully navigating the sometimes conflicting demands of these two groups – the just about managing and the most vulnerable – is the conundrum now for the Conservative party. When David Cameron set out his vision for his government weeks before the referendum result that resulted in his departure from office, he put his focus squarely on the latter group. He said his government’s mission was to “rescue a generation from poverty and extend life chances”. It may sound similar in tone to May’s opening speech, but the two prime ministers are talking about distinctly different groups, with significant ramifications in terms of policy and government activity.

Policies aimed at one can upset the other. An example is the national living wage. Surely this is universally popular? Focus groups that I ran during my time at No 10 showed that many in the just about managing group felt it was unfair. They had worked for years and years without a pay rise, albeit on a higher wage, but spoke of seeing brand new staff entering and immediately getting a significant pay increase due to the new rules. The same went for changes to the personal allowance: though popular with working-class strugglers when framed as a tax cut for them, many saw it as a change aimed at someone else. This highlights the difficulties of juggling these two groups – go too far one way and the Conservatives risk marginalising their new voters, go too far another, and they risk looking like the “nasty party” all over again.

This trade-off is not a zero-sum game. But policy, and the communication of it, is a world of prioritisation, and the instinct to gear policy towards the most vulnerable is very strong across the civil service. Some of this is down to policy reality, some of it orthodoxy, some of it political pressure. In 2017, May’s government tried to create a new category of “working-class families” in the Department for Education’s measurements of school performance, in addition to those children on free school meals. The pushback was intense, at both political and official levels, and after the general election the changes ended up being abandoned. If No 10 wants to turn more attention towards working-class voters, it will need a relentless focus to overturn these default instincts.

The central power of No 10 and the force of Johnson’s senior aide, Dominic Cummings, may mean there is an opportunity to do so. Ministers who instinctively “get” the importance of these voters are important – the chief secretary to the Treasury, Rishi Sunak, and Home Office minister Brandon Lewis jump out as examples. Though there may be changes in the machinery of government, the Treasury will be key, especially in the run-up to the next budget. Ultimately the chancellor will still hold many of the levers of policy, and if action to help working-class strugglers is going to dominate a budget, then the chancellor – who will be up against a resistant set of officials – will need to consistently champion such an agenda.

The cost of living is an area where policy can make a difference, particularly in relation to energy, fuel (this group overwhelmingly drive rather than get public transport), and food (the increasing expensiveness of “the weekly shop” hangs over them). Better funded and more responsive public services with less bureaucracy are important. There are policy areas that can address both the just about managing and the most vulnerable too, such as tackling rough sleeping and homelessness – a concern for all voters who have seen it increase dramatically over the last few years.

It is a tightrope, and it belies a quiet tension in Conservative ideology over the last decade: between Cameron’s “life chances” and May’s “just about managing”. What Boris Johnson does will determine whether his electoral coalition is a fleeting one to deliver Brexit, or whether he remakes Conservatism for good.

• James Johnson is a political adviser and former Downing Street pollster