Alright! After a lot of googling and persistence I got it working. With the new screen connected I did a full factory reset from the bootloader, turned the phone off, disconnected the battery for ~ 30 seconds, reconnected it, switched on and hey presto, good as new :-)

Yes, hopefully is just a bad screen as that would be easy enough to resolve. Waiting to hear back from support now.

I just followed the guide with a replacement screen from ifixit and sadly it is not touch responsive though the picture is fine. I've tried wiping the cache and erasing all data from the bootloader with no success. Touch is still working with the original screen. Has anyone else had this problem?