I think I have got the bulk of this right.
I have created recordsets that get the email addresses from the database.
I have set the checkboxes up as suggested;
<input name="email" type="checkbox" id="Chairman" value="<?php echo((isset($_POST["lsdogs_chairman"]))?implode(",",$_POST["lsdogs_chairman"]):""); ?>">
I have configured UE to retrieve the email addresses from the checkboxes etc.
I just can't figure out what to do next to get it to work. - I guess the email addresses need to be sent to the checkboxes some how?