Regulations around elections

[xgipper]

Hi
I'm involved with a community website in the UK, and don't have formal journalism training. I'm interested to know, perhaps from someone who has, whether there are any legal restrictions on what can and can't be said (apart from the usual libel issues) around UK council elections.
I've heard of the idea of 'purdah', which I believe applies to councils themselves so they are not able to favour one party over another at election time, but is there any other requirement for the media to be 'fair' and to give each party/candidate an equal say, for example, or to not criticise a particular party/candidate in the run up to an election?
And would this also affect 'blog' type comment items on an article?
Would this situation differ in any way for general elections?
Many thanks for any information or pointers!