Hi Lewis
Send in any additional evidence to HMCTS quoting your Name and NI number on each additional page.
I usually send in a covering letter detailing what additional documents I am sending, send the letter by recorded delivery. As you are quite close to the hearing date I would contact HMCTS and let them know you are sending in additional evidence by RD so they can add the information to your file, make sure you ask for the name of the person you speak to on the phone.
Gary
Nothing on this board constitutes legal advice - always consult a professional about specific problems