If you are a PMI member, but haven't yet joined the PMI UK Chapter go to the main PMI web site and log in. Your user name is your PMI membership number, unless you have changed it. If you cannot remember your password, click on “I forgot my password” and an email remainder will be sent. This usually takes a few seconds to arrive.
Click on “Marketplace” then “Community Membership” then “Chapter” and select the United Kingdom Chapter.
Click on Join and follow the process to pay.
Current costs for PMI UK Membership is $40 USD and is free for students in full time education.