Global issuance of the complex debt securities at the heart of the credit bubble has collapsed in the wake of thousands of ratings downgrades this year, cutting huge revenues from the biggest investment banks.

The volume of collateralised debt obligations, which pool together bonds, loans and other debt, sold in the first half of this year is equivalent to just 10 per cent of the volume in the first half of 2007, according to the latest data from Dealogic and Total Securitization.