I've tried adding the date.timezone directive in the main php.ini file, which I've located in /etc/php.ini I've also verified it's location by using phpinfo();.
This is exactly what I added:
date.timezone = "Europe/London"
I then restarted nginx (service nginx restart), but when I go echo phpinfo() again the timezone still states UTC which I believe is the default timezone and roundcube won't let me install until I set a timezone, any ideas?
EDIT Just stopped nginx, started apache and the timezone was set correctly. So this must be nginx specific.
Not sure what was wrong, but I believe nGinx may have been misconfigured. Stopping the service and running Apache solved it, but that was only temporary. Just thought I'd post to let everyone know.