Fuel...
well, not followed every item, but one and a half Radar pattern comes up to about 30' fuel. Remember it's calculated in the holding, and you'll wonder how much you need for a G/A and another 20 NM final (yes, pretty close to a ton, specially with flaps extended expecting a quickie...) and this with a final reserve of a few hundred kilos more than a ton. Not to mention if you need Anti-Ice...
Okay, what we can do legally (according JAR) will lead aviation sonner or later into a situation where a lot of planes are over a closed Destination first, with unconfortable fuel states, and then the same planes queing with even less fuel over the alternate.
I hope not to be part then on the scenery, but who knows.
In adverse wx-conditions i even take fuel in excess of the max landing weight to cover delays...as mentioned before, EGLL is a good example.
(By the way, the ATC in London deserves my respect for managing that lot of traffic, however, if the smallest thing happens (e.g. one holding area u/s due to TS), delay is unavoidable...but's not your fault. Thank you guys)