Nearly half of the companies in the FTSE 100 blue-chip index and nearly two-thirds of the biggest companies listed on US stock exchange Nasdaq are failing to answer emailed investor enquiries, according to a new survey, which comes at a time when corporate transparency is in the spotlight.

The survey, by London-based technology public relations firm Rainier PR, found that of the biggest 100 companies on each of Nasdaq and FTSE, only 38 of the US-listed companies "responded to a staged emailed investor enquiry with the appropriate answers, while just 53 FTSE 100 companies responded within a three-week period".