In a recent note to investors, the multi-asset fund manager said US government bonds have made "suspiciously high returns", having been seen as the "definitive safe haven asset" over the last three decades, and warned that the low-inflation, low-rate environment is set to be dominated by hawkish central bank policy for some time to come.
"In this inflationary environment, US Treasuries, far from being safe haven assets, have been one of the primary expressions of inflation risk," he explained. "As a result, US Treasuries and many bond sub-asset classes have experienced losses over the recent period, as a more inflationary environment is seeing nominal assets like bonds struggle."
Crypto overtakes gold as 'safe haven asset' amid Ukraine crisis
In contrast, Rayner said the "risk hierarchy gets turned on its head" during an inflationary environment, arguing that inflation-friendly assets such as equities, commodities and properties begin to serve as lower-risk assets "in a relative and absolute sense".
"The importance of considering how assets behave in relation to each other should not be underplayed, especially in the wider context of diversifying portfolios," the manager said.
While US Treasuries and gold - another stereotypical safe haven asset - have performed well recently as a result of the Ukraine crisis, he pointed out the conflict has only further served to exacerbate global supply chain squeezes and subsequent inflation risk.
"This has further increased the momentum for higher inflation and it has muddied the waters for central banks by increasing stagflation risk," Rayner reasoned.
"In our opinion, the structure of what low risk means is changing. As a result, low-risk portfolios need to change too.
"For global multi-asset funds, especially in the perceived lower risk IA Mixed Investment 0-35% Shares sector, we believe that a pragmatic mindset and a liquid portfolio are helpful attributes at times like this because what has been low risk in the past might well not be in the future."