Although it was the “Brexit election” Boris Johnson wanted, the Labour, Liberal Democrat and Green parties would be foolish to view his success as a one-off.

In his victory speech, Johnson made clear his top priority would be to cement the support of the many working-class people who had voted Conservative for the first time. He acknowledged many had merely “lent” their support to his party because of Brexit. Indeed, many did not think they were voting Tory – they were “backing Boris”.

The scale of Johnson’s majority does not merely mean Labour has a mountain to climb to win in five years’ time. The party will probably need two more heaves, at least – even with a new leader. We now face the prospect of another decade of Tory rule, a longer spell than the 18-year Thatcher-Major era.

Johnson said something significant about his party as he celebrated his triumph: “In delivering change,” he said, “we must change, too.” This is normally what the vanquished says, not the victor. On the one hand, the prime minister has no reason to be worried. In demolishing Labour’s “red wall” of constituencies running from north Wales to the northeast, he can claim to head a genuinely One Nation Conservative government that enjoys (for now) the support of people in all social classes.

Yet on the other hand, Johnson should be worried. His words show a recognition that, to keep their grip on power, the Tories not only have to “work night and day, flat out” to prove right the people who voted for him this time, but to win over those that did not. Specifically they will need to do better among younger voters, as well as the black and ethnic minority people who make up a growing proportion of the urban electorate.

Meanwhile, newly elected Tory MPs will be loyal to Johnson, knowing they owe their new job to him. But they will become champions for their constituencies. That will force Johnson to pursue a more interventionist regional policy, in order to bridge the divide between London and other parts of the country.

Although Johnson described his project as “sensible, moderate, One Nation conservatism”, his manifesto was deliberately opaque on domestic policy. Allies predict the liberal “London mayor Boris” will now take over from hardline “Brexit Boris”.

That won’t be as simple as it sounds: Brexit will not be “done” next month, and Johnson will not be able to fudge the UK’s future relationship with the EU much longer.

Even Tory insiders admit they are unsure who the real Boris Johnson will be when he finally stands up. They see a pragmatist interested in power who will not align with either his party’s libertarian wing or the traditional left, but try to straddle both.

The challenge for Johnson, in other words, is to turn One Nation from a slogan into a strategy. Will he finally pay more than lip service to the 48 per cent by shifting to a softer Brexit? Will he acknowledge that in this election he did not win the majority he would have needed in a Final Say referendum?

The threat to the union might make a mockery of his One Nation mantra. For the first time in history, Northern Ireland has more nationalist than unionist MPs. Economic gravity might pull the province towards a united Ireland. The SNP’s gains will fuel demands for another independence referendum; Johnson might not be able to deny one forever if the party wins a majority in the 2021 Scottish parliament elections.

When Brexit is eventually “done”, holding our one nation together might prove Johnson’s biggest challenge.

Andrew Grice, The Independent