The loft was insulated, at some time in the past, with ‘Clinker’, which is defined as:
A local term used for remains of coal that have burned and the surrounding rock that has been transformed during the burning of the coal.
In other words, the Victorians and slightly later folk thought it a good idea to throw coal dust up there every now and then for good measure.
We filled 21 bin sacks full of the stuff. Never, ever been so filthy.
Now installing some kind of space-age (ha) insulation...