Via a tweet from the inestimable Tom Watson. My additions in brackets.

1) Blog as yourself
2) Own your own content : “The content of this blog is my own and does not reflect the opinions of my employer”
3) Be nice
4) Keep Secrets
5) No anonymous comments
6) Remember the Civil Service Code
7) Got a problem? Talk to your boss. (Or the appropriate Comms team)
8) Stop it if we say so. (Individual posts or the whole thing)
9) Be the authority in your own specialist field – provide worthwhile information
10) Think about consequences
11) Media interest? Tell your boss. (And the Comms team)
12) Correct your own mistakes

Give the sensible attitude of the various Comms teams in not giving hard-and-fast rules of what can be written about number 8 is the important one to remember.