Sorry I have been offline and not around when this question was asked.
Here we go with my answer.
There is a seperate certificate that you have to issue just for any work involving emergency lighting. This includes additions, or new installations. It is far more complex than an eic. There is also a seperate certificate for periodics on emergency lighting.
Both certificates are not deemed to be valid without a BS7671 certificate on the circuit(s) that supply the system. It is also a requirement that on completion, training is given to authorised personnel as to the testing methods used, and the completion of log books which should be supplied by the installer.
Also when it comes to testing you have to enter on the emergency lighting certificate a deviation if you use the standard sign height and distance method of valuations.
I see many installations where the requirements are not fully met, but pass the gauntlet, until some eagle eyed fire official decides its not up to standards.