How much debt is too much? After three economic shocks in a row – the financial crisis, the pandemic and the energy price spike – the world economy is drowning in the stuff, with little sign of any life raft to the rescue.

It’s true that, relative to GDP, we’ve seen still higher levels of public debt in the past, the last such occasion as a result of the Second World War. It’s also true that the Japanese economy has managed to coexist with debt to GDP of more than 200pc reasonably well for many years now.

But don’t let these much quoted examples of “debt doesn’t matter” lull you into a false sense of security. High wartime debt was tolerated because everybody knew that military spending would fall…