I have a disgusting smell in my living room cupboard.
Ive had my loft chemically cleaned due to the hatch being broken,no bird poo.
Ive had a Scottish Gas check for a leak,no leak.
Ive got a plumber and a slater coming out to work together to see if they can find where the smell is coming from.

Dead mouse or bird behind or under the cupboard, or in the wall or ceiling, maybe. Awful smell for weeks.
In ceilings they leave a brown stain about 3" across.