@Snog
I'm bewildered as to why some offices don't allow sandals in the summer. I don't think it's unprofessional in any way to have your toes on display?
Schools (well, Secondary at least) usually have the No Sandals, No Strappy Tops, Shoulders and Cleavage Must Be Covered at All Times rules. In summer, they might let a sleeveless blouse slip through if it covers everything else and is clearly a blouse, rather than a sleeveless top - preferably if you wore a camisole underneath if it happened to be less than totally opaque. They're not keen on bare legs, either, but usually turn a blind eye for staff who have perfect, tanned legs (as they did for the skirt length requirements in the Staff Handbook).
One I worked at insisted upon blazers (and ties for men) being worn by all staff at all times, too. Including the Parents' Evening in the sun trap hall. When the heating malfunctioned so it was on full blast for the hottest day of the year.
I could go along with the no sandals rule because 2000 lumpen teenagers thundering around was a recipe for broken toes and the last time I was in A&E in a heatwave (injured hand), I was surrounded by people who had not only done hideously painful things to toes and ankles whilst wearing flip flops, sliders and sandals, they all seemed to have little concept of ongoing footcare or correct sizing, going by
a) the smells
b) the state of toenails
c) the state of the skin and calluses on their feet
d) how many had heels and toes hanging over the edge and out the sides of their too-small sandals
I'm by no means high maintenance, when I do have to attend due to an ongoing ankle thing (arthritis related), I did at least have clean, tidy feet and toes because I try to look after them properly, with help from DP when the arthritis makes things difficult.
Nobody needs to see or smell that at work.