My wife and I are English, although we live in the US. My wife's claim to belong to Clan Davidson is that she was told as much by her Scottish maternal grandmother, maiden name Davidson. That's good enough for me.

Callaghan is my mother's fathers family name, and also the title of one of only a dozen Irish clan chiefs recognised by the Irish government, when they used to recognise such chiefs. This was almost certainly always unconstitutional, as the Irish constitution forbids recognition of titles of nobility, which is rather ironic, as it does not exclude Irish titles.