The survey by law firm DLA Piper Rudnick Gray Cary also found that a third of companies would not tell their press offices if they were under investigation.
Moreover, three quarters of companies had not informed their security guards of procedures to deal with an investigation, during which the FSA and DTI can use force to enter buildings.
Around 54 per cent of firms had not told their reception staff how to deal with these situations.
The report said the results raised 'serious questions about the way companies communicate these issues'.
DLA legislative and regulatory group head Neil Gerrard said companies' understanding 'of the complexity of regulation was still lacking'.