Thanks for the response Chris,
As of right now everything is working, I'm a little hesitant to reboot in case something goes awry again, but for now all is good.
In the end I did the following:
* Updated the BIOS
* Configured the BIOS to disable switchable graphics (which means AMD card is used)
* Updated AMD drivers
* Unistalled Dell monitor driver
* Plugged the monitors into the docking station, then ran the DELL Monitor driver software - it detected both monitors and installed the software.
* Things still weren't 100% with the dodgy monitor - but I tweaked the DisplayPort 1.2 settings and its now working. (If I got to the OSD the 'display settings' show Display Port 1.2 > Disable).
I've put the laptop to sleep overnight and it work up and all the monitors came back on (yay), but I'm yet to do a reboot since I got things working.
I'll close this issue though as of right now things are working. Thanks for the suggestions (as the various testing that I was doing based on your suggestions led me through the above steps to get it working).