A bit more digging through myriad similar issues I found this bug https://bugs.launchpad.net/ubuntu/+source/eject/+bug/412527 which had a suggestion to change the SCSI setting in the BIOS. I did this and my system is now back recognising blank media. As mentioned by someone else in the thread - not sure if this has any other side-effects but at present all is working ok and I can now burn DVDs once again.
A bit more digging through myriad similar issues I found this bug https:/ /bugs.launchpad .net/ubuntu/ +source/ eject/+ bug/412527 which had a suggestion to change the SCSI setting in the BIOS. I did this and my system is now back recognising blank media. As mentioned by someone else in the thread - not sure if this has any other side-effects but at present all is working ok and I can now burn DVDs once again.