AA already offer the facility (very clearly at payment stage) to confirm a booking but put it on hold for up to 5 days. This allows people to make two separate bookings without committing to the first one before the second one is also confirmed. In my opinion this is better than a 24 hour cooling off period. Secondly, it’s very simple, don’t assume a booking is made if the website has not generated the 6 digit booking reference and write it down. I agree with HarryMonk.