apt-get update and synaptic today produced a load of errors when I tried to update 12.10 e.g _cache->open() failed, please report.

I use the following in the terminal to update Ubuntu 12.10 in the terminal :-
"sudo apt-get update && sudo apt-get dist-upgrade && sudo apt-get autoclean"
Today this resulted in the following errors :-
Reading package lists... Error!
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://extras.ubuntu.com quantal Release: The following signatures were invalid: BADSIG 16126D3A3E5C1192 Ubuntu Extras Archive Automatic Signing Key <email address hidden>
W: GPG error: http://archive.canonical.com quantal Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key <email address hidden>
W: GPG error: http://gb.archive.ubuntu.com quantal Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key <email address hidden>
W: GPG error: http://gb.archive.ubuntu.com quantal-backports Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key <email address hidden>
W: Failed to fetch http://extras.ubuntu.com/ubuntu/dists/quantal/Release
W: Some index files failed to download. They have been ignored, or old ones used instead.
E: Encountered a section with no Package: header
E: Problem with MergeList /var/lib/apt/lists/gb.archive.ubuntu.com_ubuntu_dists_quantal_main_i18n_Translation-en
E: The package lists or status file could not be parsed or opened.

Any advice on resolving this will be much appreciated.