Hi, many thanks for the reassuring response. Yes, I did see from examining the Apache error.log that each time it fails it seems to be looking in /config/ for config.ini.php, which as you rightly identify does not exist, and is only created further down the installation routine. As such I'm going to continue with the installation and see how it rolls out, I will report back.
For info we are installing to Ubuntu 14.04.4 LTS.