In what circumstances will a mortgagee in possession of a coal mine be held liable for severance and/or severance of the mine's assets?

In Taylor v. Mostyn (1886) 33 Ch. D. 226, 55 L.J. Ch. 893, Plaintiffs, mortgagees in possession of a colliery, and also lessees of the same colliery for a fixed term at a rent and royalty, made a sub-lease of the mines, and gave their sub-lessees licence to work and remove certain pillars of coal in breach of the covenants in the superior lease. and it was held that in taking the accounts against them as mortgagees in possession, they must be treated as having removed the coal themselves; and, having done so wrongfully, were liable as trespassers to account, not for the amount of the royalty payable for coal gotten under the lease, but for the full value of the coal less the costs of raising it, without any deduction for the costs of severance.