While Sile was putting in some plants in the back garden tonight she found this button.
This is a very bad shot of it (I will substitute it with a better when the daughter Caitriona comes down next) but you can read that it says George V and Royal Engineers.
This makes it a button from an army uniform of at least pre 1936. (George V ruled between 1910 and 1936)
This is just exactly about the time the house was built, so is unlilely to be contempory, that leaves one with two alternatives.
Either it was carried into the house, as a souvenier, as it was built.
Alternatively it had been lost on the land before the house was built at all.

Either way I feel at least one short story coming on me.
Watch this space!