When UK regulators probe what private assets are really worth, they are likely to find a mix of rigour, guesswork and wishful thinking, industry insiders say.

The Financial Conduct Authority is expected to begin its review this year — a critical moment of scrutiny for a sprawling asset class that pension funds and other investors piled into as they hunted for returns during the long era of low interest rates.

Tracking the value of publicly traded stocks and bonds is easy. But private debt and equity and assets such as real estate and infrastructure are generally valued manually, and quarterly, using a wide range of techniques. Academics at business school Edhec wrote in a consultation paper submitted to the UK government last month that some of those methods for valuing infrastructure are “akin to fraud”.