Thanks Kevin, but it looks like I'm not the only one with the disconnection issues.
community.office365.com/.../157621.aspx
This is happening on my other Mac at home, and having been using Office3 365 since last year, this is a completely new issue, so I don't believe that I should remove and then set up the accounts again. On saying that, I have tried this, and the issue persists.
All I'm hoping for is that someone is looking in to the issue so I know it will be resolved at some point. Outlook is effectively unusable if I can't rely on it to be opened and waiting for emails coming in.
Thanks
Andy