Hi wani,
The precedent overruled in BRB v Herrington was Addie v Dumbreck. You can find the case here:
viewtopic.php?f=84&t=628The principle concerned the duty of care owed to a child trespasser. They overruled it because of changing attitudes towards responsibility and children. It was thought that in a modern society land owners should ensure their premises are safe or take steps to stop children coming on to their land. This came under the principle in the 1966 practise statement relating to justice and to allow the law to develop.
A public Bill becomes law by going through both Houses of Parliament and the process of the different readings then getting Royal assent as described here:
http://www.e-lawresources.co.uk/Statutes.phpWhat course are you doing? I'm doing a level.