Hi, Stuart.

>I have been asked to look at setting up some sort of blogging site, so that offices around the country can help each other with problems and they get feedback on bugs, suggestions ect. , as usual my temptation is to write my own, but I can’t believe that there are not thousands of suitable solutions out there already. The only proviso is they must have strict control of who has access and what is written.

Is it a blog what you need? It sounds to me more like a Wiki...

Also, you may check Google Apps for Domains, where you can set up a huge number of services, including Google Sites, which are like an Über-Wiki service:
http://sites.google.com/

Regards,