It's good to know about that internal form and the extra three-quarters of an hour to get few thousand out.
One of the tips if you have the time for it is to stagger the withdraw over 4 or 5 day at £400-£500 a day if say you needed £2G
Don't know if this still works on ATMs but I used to do one withdraw at 11:55pm and a 2nd at 12:05am