The Permaflex incident led to section 21 (disclosure of information) of the FP Act being amended to allow Fire Service officers to divulge information to the HSE. You may find further information in FP Act circular No. 10 (issued 7 December 1981), which refers to this incident and Appendices to this circular give further clarification. If it helps, I will give you a couple of quotes:
'There is authority for the proposition that it suffices to prevent the place from being excluded from the factory if a process is carried on in the place, or is a process which is incidental to what is done in the main factory, (Powley v. Bristol Siddley Emgines Ltd. (1965) ALL ER 612', from Appendix 10/1, and:
'3. The following types of warehouse are likely to be subject to the appropriate 1976 Statutory Instrument by virtue of being a 'factory' premises....
(b) a warehouse situated in a separate building within the close or curtilage of a factory, unless the warehouse is solely used for some purpose other than the processes for, and incidental to, the factory....' from Appendix 10/2.