The use of the ALARM missile is not secret and there are numerous references to it both on the Internet and in books. For example, you can read something about the missile here, or on this site.
You should note that the Marconi radar seeker, used to guide ALARM, was upgraded under SR(A)-1247. Therefore, even if the "restricted" document in my case was linked to ALARM, it is now obsolete.
I would welcome any comments from readers who know anything about this upgrade, or who can give technical assistance to help me identify key stages in the development of the ALARM seeker in the 1980s. I need to establish whether the "restricted" document was ever used on ALARM, or was it related to some completely different project. Anonymous comments are welcome, as I have no wish to get anybody into trouble for telling the truth.