Is a tourist (a UK national) able to obtain their tourist visa on arrival in Luxor, even when their plane lands at about 22:30? Will the visa office be closed then, or anything awkward like that?
Visas are available from the many bank kiosks in the arrival hall. They are next to each other along the left wall as you enter the airport terminal building.
They will only accept notes, not coins, so you have to offer the next highest amount using notes. As long as the £ is worth more than $1.25, offering a British £20 note (each person) will get you a visa and some change in egyptian currency.
... which implies that you get them from staff.