Thanks to Simon Patton for alerting me to this:
Pre-entries are bring taken at the SportIdent website https://www.sientries.co.uk/event.php?elid=Y&event…. They say “This event uses pre-selection lists to allocate entries. To get a pre-selection list entry just enter as normal. No payment is required at this stage as there is no guarantee of being offered a place. If the Event Organiser is able to offer you a place they will send you an email inviting you to enter. You will then be asked to come back to this site and make your payment to confirm your entry.”