If you get the following error during apt-get commands
rr http://gb.archive.ubuntu.com natty-backports Release.gpg Temporary failure resolving ‘gb.archive.ubuntu.com’
Then there is a name server issue.The source list is not correctly resolving.So you have to check the DNS settings or name server settings in /etc/resolv.conf
So open /etc/resolv.conf in your editor and add nameserver
Then use the command apt-get
This would probably resolv the issue.