Old Czech composers, current German MS owners and restrictions on use: can you help?

From the Concerto for Oboe and Bassoon in F major
by Antonín Reichenauer, who died in Prague in 1730

One of the 1709 Blog's readers has written to ask as follows:

"I am a musicologist and occasional performer of pre-1800 music. Copyright is seldom an issue in dealing with old musical manuscripts as the copyright protection (on the whole) has long since expired on such musical works. I understand that the owners of musical manuscripts, for example, maintain some rights on the reproduction of those documents in facsimile. I have been in contact with the music manuscript department at a well-known library and in terms of recordings, they couldn't find a reason that owning a music manuscript from the 18th century afforded the owner any copyright protection (at least under UK law) for an audio recording.

Here's my question: what is the legal status of the modern German owner of a musical manuscript that was composed by a Czech composer in the 1730s (without any kind of legal bequest from the composer to the owner)? The owner of this manuscript made a facsimile of that manuscript available to the public (in a public library in Germany) but with the explicit understanding that no audio recording would be made without the owner's permission. However, I don't see that the owner (despite demanding such a signature in order to get a photocopy) has a legal leg to stand on. If there is no copyright on the music and no physical reproduction has been made (facsimile or modern transcription), could the German owner conceivably sue someone in the UK for making an audio recording of this music?"

Readers' responses are very much welcome -- on the understanding, naturally, that they do not constitute legal advice.