You can request (and if granted, hold) slots on a provisional basis pending grant of an OL. You do need a designator, for which you have to pay a fee, to request and hold slots though. You also need to pay a fee with your OL application…
They’ve been at this for nearly a year.
Brave people indeed launching with ATRs given the current problems afflicting virtually everyone else operating them right now. The only thing I did wonder is if they are going to buy part or all of another UK operator already with ATRs in its fleet that don’t seem to have very much work.