Harold Macmillan once said “at home, you always have to be a politician; when you’re abroad you almost feel yourself a statesman”. That is what Boris Johnson will have felt as he hosted the G7 leaders in Cornwall – a chance to step back from some of the daily pressures and consider the big issues facing the world.

In my case, the closest I came to that kind of meeting was at a breakfast in New York for the permanent members of the UN Security Council – the foreign ministers of five of the most powerful countries in the world sitting around a table talking in total frankness in a forum that has never leaked.

When you represent your country on such occasions, you ask yourself about our role in the world: is Britain really just a minor player, marginalised by our departure from the EU and dwarfed by the rise of new economies, as some would have us believe?

Or is there a major role for us to play in a world which faces so many challenges new and old?

If the latter (as I believe) where is the hard evidence we are capable of playing such a definitive role beyond a patriotic desire for influence?

I found as foreign secretary that, perhaps surprisingly, Britain has continued to exert global influence despite losing its empire and economic dominance. This is because, at our best, we have always stood for values and causes bigger than ourselves, for ideals shared inside our own shores but also widely beyond them.

At the top of the list of such ideas are democracy, the rule of law and respect for human rights – but in a modern context you could add tackling climate change, tackling pandemics and global poverty.

We must always, of course, defend our narrower interests, whether commercial, territorial or diplomatic – and there are sometimes trade-offs when doing so. But because we have usually been willing to embrace causes beyond purely national interests, we have acquired an authority on the global stage that is about much more than history.

Britain thus remains one of the surprisingly few countries that has both the global reach and political traditions that allow us to go out to bat for universal principles. And we achieve that through a unique combination of hard power and soft power, alliances and trade, every one of which embodies and promotes our values, backed up by our superb diplomats.

This year the big global challenge on the table is climate change. COP26, which I negotiated for us to host when I was foreign secretary, is the last chance we have to set the world on a path to net zero before we hit a climate tipping point.

As the first country to make net zero legally binding, under Theresa May, we start with considerable authority.

Being able to show – as we can – that the electricity we generate from coal has reduced from 40 per cent to less than two per cent since 2012 matters when you are trying to persuade other countries to be equally ambitious.

But we cannot succeed in such tasks alone. That depends on building an alliance of countries that share our goals.

In the case of climate change, it will particularly depend on China which has now committed to net zero by 2060 but remains vague about how it will get there.

Relations with this rising superpower will inevitably remain complex as we seek to deliver another essential objective, namely the ongoing security of democracies and open societies.

To play a global role we will need the diplomatic persistence and ingenuity for which we are well known.

But post-Brexit we will also need something else: a rediscovery of quiet British self-confidence about our ability to make things happen across the world.

Our track record of doing so is second to none – alongside America we built a global order that has led to more freedom, more prosperity and less conflict than any other.

This century, too, if we are prepared to be ambitious, there remains a vitally important global footprint for our small island.