Cupboard in chimney breast

I want to remove the 30s tiled fireplace in my dining room and line the space behind in order to create a cupboard. The chimney breast is soft Norfolk red brick, about 4 foot wide, in a turn of the century Norwich terraced house. What should I line the space with? Can I use plaster board or some other product? I think soot is corrosive and might seep through if I just render/plaster it. Do I need to use a chimney balloon as well? I'm tempted to get proper help and open up the space to nearer the ceiling (the house is tiny), but this would need a new lintel and all sorts doing. Might cost a fortune… Has anyone else done this or got any advice?

Unused chimney flues should ideally be fitted with a vented cap at the top to prevent rain & stupid birds entering & a vent at the bottom to prevent damp; IMO, installing a cupboard inside one is not a good idea.