You can join in one of two ways, depending on your tech. Below is an online form you can fill in. Alternatively you can download a form, print it, fill it in, and post it. All you need to know to do it this way is on the form. See the panel on the right of the page (or bottom on small screens).
Alternatively, please complete the following screen form, and then pay, either by paypal (see panel to the right or bottom of this page), bank transfer, or cheque.
Pay by Paypal in the panel to the right or bottom of this page.