asked the Secretary of State for the Environment what are the criteria used by local authorities to determine whether or not derelict land justifies treatment.

For the purposes of derelict land grant, "Derelict land" is used to mean land so damaged by industrial or other development that it is incapable of beneficial use without treatment. Whether or not treatment is justified depends on the nature and situation of the dereliction, its effect on the environment and practicability of reclamation works. It is essentially a matter for local assessment.