Diggle said the prospectuses for the Government's power companies were the size of telephone directories and he doubted many retail investors would have read them. "All of those documents were so full of jargon, even if you went to the glossary, and some of those ran for pages."
But he stopped short of criticising the firms behind the prospectuses.
"We wouldn't criticise the promoters. They have been working in the framework set out for them.
"Promoters have been constrained by what the regulations have told them to do," Diggle said.
New requirements for disclosure documents are due to be introduced next year under the Financial Markets Conduct Act - a major re-write of securities law. The changes won't be fully in force until 2016.
Diggle said it could not come soon enough for retail investors who were not a priority under current law. "The focus has been industry focused, based around technical experts."
The change in legislation would provide retail investors with options, he said. "They can read the slimmed-down version and then can make a decision on whether they want to know more about it or not."
Ross Pennington, a securities lawyer at Chapman Tripp, said the timing of the FMA report was surprising and the criticism a little unfair, "given a large part of the reason disclosure documents are as they are is down to defects in the current regime".
He said: "The vast majority have been identified and will be fixed".
Under microscope
Prospectuses since June 2012
* Fonterra Shareholders' Fund
* SLI Systems
* Wynyard Group
* Z Energy
* Mighty River Power
* Meridian Energy
FMA findings
* Offer documents too long.
* Branding should not dominate.
* Risks are not ranked in order of significance.
* Financial information needs to be given clearly and effectively.