I've provided a slightly longer answer in your other thread. However there is no specific guide which says when you need to get permission or where the normal rules of fair use or fair dealing will keep you out of trouble. Perhaps the best place to seek more detailed help is the Copyright Licensing Agency who are specifically set up to work with academic organisations on copyright matters. They even have a search facility to allow you to check particular works or authors. However you need to be aware that the CLA is primarily aimed at issuing licences so they may advise that this is required for your particular purpose, even though others might say that a licence is not strictly necessary.