An inflation comeback coupled with rising unemployment is an economic rarity last seen in the 1970s, but economists warn it could be back with a vengeance, threatening to upend a failsafe for investors.

The strategy of investing 60 per cent of a portfolio in stocks and 40 per cent in bonds – known as the 60/40 portfolio – has historically ensured good returns in any economic environment because the two asset classes typically move in opposite directions.