With regard to last Thursday I have had a sudden recollection which must have been blanked from my memory due to stress.
Although the weather at the field was fine there were large thunderstorm cells moving all around. There were sector restrictions north and south of us due to the weather and for over an hour every departure needed to avoid to some degree. That meant instead of being able to launch a departure every 60 seconds, they were all going 2 minutes apart. I don't know what the approach situation was like but when there are cells around the stacks there can be major issues. All the holds in the TMA are separated upto FL150 but this is only the case when aircraft are within the designated holding areas flying the published holds. When holding starts getting more random ie, "can we hold 2 miles south of biggin or go left instead of right" then the whole thing can go out of the window. Rather than having 9 at Ockham and 9 at Biggin, if they are no longer separated then they have to share the levels which means 9 total. As you can imagine this has a major effect on the holding capacity and therefore inbound delay.