That's much more likely to be a telephone bell.
The GPO equivalent is arguably this
which was a "feature" covered in paint, when we moved into this house. I retained it for the same reason as your son-in-law, but now you and he knows what it is perhaps he will want to use it for it's original purpose?
It would have been a brave person who would have connected a foreign bell to the telephone network pre-deregulation, the genuine article would have been subject to a monthly rental.
Start another thread in the Telecoms section if you want more information, and how to connect it.
<EDIT> here's a pair of them in another auction, correctly described.
https://www.the-saleroom.com/en-gb/a...7-a5bd010b20fa