Tanned and relaxed after a week in Mustique, Boris Johnson returns to the office this week as the most powerful Tory prime minister since Margaret Thatcher.

With Labour’s electoral coalition fractured perhaps beyond repair, Mr Johnson will believe he now has a decade at his disposal to reboot Britain - a job that begins with his renegotiation of the UK’s relationship with the European Union.

The outcome of this negotiation, the first phase of which is currently set to be completed by Dec 31 2020, will lay the political and economic foundations for what comes next, and yet it is still remarkably unclear how Mr Johnson intends to handle the process.

If he gets Brexit wrong, it could prove a permanent drag on his new administration. Conversely, a successful negotiation (the definition of which depends where you stand on Brexit) may yet provide a springboard to a better future.

So as we look to the year ahead, here are five big ‘known unknowns’ about what happens next.

Will Boris listen to business?

It was Mr Johnson who memorably exclaimed “f--- business” when, as foreign secretary, he was asked at a diplomatic reception about why greater consideration was not being given to the negative impacts of Brexit for British business.