Post-old gasfire removal- eitherside- old fire lining?

[hora]

Our living room used to have a huge 70's style gasfire feature (eyesore)- I removed all this to leave a small opening 11inches across with two white 'concrete'? Blocks eitherside vertically within the wider large brick opening/surround.

From what I gather this is to create a flue and is NOT usually structural? Is this true? Are they ever structural?

another question- are these blocks ever.....asbestos?

No pics as to get us into the house a plasterer temporarily sealed over the fireplace for me when skimming the walls.

If I pull these out can I expect the chimney to come down through the roof?

[welsh brickie]

Hi
No its not structural,Its the fireback you can remove it its non toxic,but wear a dustmask and gloves because of the soot.