The 'Sporter' and NSRA websites have all the details. It was originally created for juniors, but there is an 'open' category for any age.
http://www.sporter.org.uk/
http://www.nsra.co.uk/index.php/home/reference/rules
I was going to have a go myself, but never got around to it - life keeps getting in the way!
A number of manufacturers produce rifles tailored for this discipline, they are not the leery creations used in 10m precision, but I think any rifle that meets the criteria in the rules can by used.
Hope this helps.
Mark.