The complex structured funds that dominated investment in risky loans to private equity buy-outs have been put under greater pressure after Moody’s said it had put the vast majority of the market on review for ratings cuts.

The agency said on Wednesday that all apart from the most senior bonds issued by every collateralised loan obligation (CLO) it had ever rated faced downgrades due to changes in the way Moody’s assesses the riskiness of these investment vehicles.