You can just pay with cash at the counter.  You don't have to be a member.  Safety notes here.
http://www.bayercropscience.co.uk/assets/Uploads/Cadou-Star-label3.pdf

How much ground do you need to treat and what state is it in now ?  If it's already weedy, you'd need to get rid of the existing weeds first or else it would be a waste of time using capa.
Email me if you want to chat one to one.