What's this?

[SparklySneakers]

Outside kitchen wall of my mum's house. Is full of plastic and insulation.

Hobbit coal hole? Or more likely a manually operated vent perhaps.

Does it open, what is on the inside wall?

It looks like an ash bin for an old open fire (baxi boiler) x

Its a chimney access door for cleaning the chimney I believe, so it can be done from a different access point? I would guess in the event something further down is obstructing it. Our chimney sweep made a note of ours but didn't need to use it... i think!

I would guess the insulation is to stop draughts etc getting through it

It's a semi detached bungalow and the chimney is in the middle of the two houses. It's about 20ft from the fireplace. Boiler was in a different room.

It sits below the floor line

How old is the house and is there a crawl space or cellar? It looks just like the chimney access points on the exterior of our Edwardian house.

It's 1930s ish. There is a crawl space, yes..

Coal hole (where coal deliveries would go)

Or, more accurately, a coal chute door.

Aha! Thank you! That makes sense

I think it's an access point to clean the chimney for a Baxi anthracite boiler.