I have the same problem, too.
It doesn't have to do with the length or width of the foot, it has to do with the shape.
Shoes here in England seem to be designed for a foot that is pretty much the same width from the ball of the foot to the heel, so the sides of the shoe form almost parallel lines. (My husbands feet are kind of like this.)
My feet are sort of V-shaped. They are widest at the toes and the ball of the foot, and then taper down so that I have a very slim heel and ankle in comparison.
The shoes that I bought in the US were all narrower at the heel, so they would pinch your foot at the heel so the shoe would stay on.
Here in the UK, if I buy a shoe that is wide enough so that it doesn't pinch my toes, it is much too wide in the heel and I just walk right out of it.
An analogy would be if you bought a pair of trousers and you have a waist, if the waist of the trousers was the same width as the width of the part that went around your hips and you didn't wear a belt, your trousers would fall off.
What I have done is stick to only wearing shoes with ankle straps or laces, to hold the shoe onto my foot. I know it limits the choices and may not allow me to wear the latest fashions, but at least it prevents me from walking out of my shoe and twisting my ankle when I'm in the street.
(I have made the mistake of thinking that I need a smaller size because the shoe wouldn't stay on when I tried on a larger size; I just ended up crushing my toes.)
ETA: What kind of job requires you to wear heels? That seems discriminatory.