In connection with the 'cash for peerages' scandal, there were a number of mentions in the press about secondary email systems, following rumours about the existence of such a system within Downing Street. Do secondary email systems exist? How do they work and why are they used? And what should lawyers and regulators know about disclosure of evidence from them?

It is not uncommon for financial services, insurance, healthcare and government departments to operate two email systems. One email system is 'open' and used for general corporate communications; the other is a 'private' system and is for the so-called trusted few.

These private systems are usually seen as a safe and secure way of communication between members who have access to the system. Depending upon the level of security required, they can operate over secure, isolated networks, they may not be connected to the internet and they often employ sophisticated levels of encryption.