Hi esctosh,
I suspect that this document was compiled by department B44 at the Filton, UK site. There is a snowball's chance of it being public domain.
You could request access to the document, but complications are that after organizational restructuring, department B44 no longer exists in its original form, and the engineering IP at Filton is now owned by EADS Airbus. Most of the people who worked there in '81 are long, long gone, but record-keeping at the site is very good. I am certain that if (a that's a big if) you were cleared for access to the document, then an archivist would be able to quickly produce an original copy.
FastMouse