Sch 1 para 12A
The judge may not issue an all premises warrant unless he is satisfied— (a) that there are reasonable grounds for believing that it is necessary to search premises occupied or controlled by the person in question which are not specified in the application, as well as those which are, in order to find the material in question; and (b) that it is not reasonably practicable to specify all the premises which he occupies or controls which might need to be searched.