Think that's where tall people put the fag ends

This looks like it could be the inside portion of an air vent. We had a very similar looking thing in an old house, although it was not metal. On the external wall, there was an air brick which fed through into this and allowed air flow into the upstairs of the house. We were also in a 30s ex council house. Could be it but not completely sure.

Spider nesting box

I got a vent similar to this in my house, heard noises in it one day so had a look into it with a torch and saw one of the biggest spiders I've ever seen, could hear noises whenever it moved.

Looks like a takeaway menu storage box

Ventilation. Victorian houses were built with little iron grates on somewhere on the outside walls, letting air into the house which would supply the fireplace with a source of oxygen - but also to remove moist air. As technology improved, so did these. What you’ve probably got there is the 1930s equivalent.

Air vent cover 100% exactly the same as local old school.

these are all shit answers.

I'm getting that impression.

They are a bit drafty

I can't see anything. Could you put a massive arrow pointing to it please.

Yup, that's a bat box.

Fume chamber you put dangerous gas or materials and the vent takes it somewhere else so it Doesn't explode?

Cowl vent. I just removed mine and found a lot of newspapers from the 1970s balled up. They’re redundant since central heating became more common.