I've clarified the situation with share.com .... I'm pretty pleased that it looks like they are proactively looking after their customers. They have also been really quick at responding to my queries so ^ to them!
Here is their response
We will be writing to all shareholders that qualify for this shareholder benefit after the record date which is in early November.
You will be asked to confirm that you wish to apply for the discount coupon and to confirm your email address for the benefit to be delivered to you directly by British Airways. A response form will be included for your convenience.
I hope this clarifies the situation for you; if I can be of any further assistance, please do not hesitate to contact me.