@devil
As always thanks for your help and advice.
I will leave my explanation of the answer to my problem on this thread to help anyone else searching the forum for a similar boot problem :
After I updated grub to 2.04-9 I kept getting this line repeated in terminal after using 'apt update':
Failed to fetch
http://httpredir.debian.org/debian/dists/unstable/InRelease Something wicked happened resolving 'httpredir.debian.org:http' (-5 - No address associated with hostname)
After a forum search I found out this appeared to be a DNS problem and on investigation realised that as part of the grub updates it was updating network manager settings.
I use dnscrypt-proxy for my dns and have added the advice :
'edit the file in /etc/Networkmanager/NetworkManger.conf and add "dns=none" under the [main] section'
[/size]to stop my resolv.conf file from being altered.After removing this line apt worked properly again.