Lending the UK government a few quid hasn’t been this lucrative for decades: UK bond yields are soaring as investors demand higher returns to lend to the UK government.

Buying bonds is usually seen as a safe, boring bet; somewhere to securely stick cash that isn’t earmarked for a more exciting or higher-risk investment — and buying government bonds is especially so. Returns for buying German bonds, for example, hovered near zero percent for the best part of a decade.But investors lending money to the UK government for 30 years can now earn as much as 5.35% a year — a record-high yield not seen since 1998 — while the yield for buying a 10-year gilt (what the UK calls its government bonds) has also hit its highest level...