The domain glenbogle.com was actually registered by the BBC in 2001 and www.glenbogle.com redirected to the official Monarch of the Glen web site for several years.
'Simon Slater (I)' (Fleming) was actually playing the piano in the drawing room scene and the following montage. He is a professional musician and composer as well as an actor.
Alastair Mackenzie (Archie MacDonald) & Anna Wilson-Jones (Justine Thatcher) also worked together on episode 1.1, The National Anthem (2011), of Black Mirror (2011) as Martin & Jane Callow respectively.