From the TARDIS Data Core wiki:Angus Ferguson MacRanald was the landlord of the Fox Inn at Tulloch, Scotland. He was fond of playing the bagpipes and was said to have second sight, being the seventh son of a seventh son. UNITused his inn as a temporary HQ while investigating the destruction of North Sea oil rigs. He was killed by Odda, who was using the guise of Sister Lamont.
('Doctor Who' - "Terror Of The Zygons")
MacTavish was an inn-keeper in the small village of Stevenage, where Simon Templar stumbled on a small but deadly community of Communist infiltrators.
('The Saint' - "The Fellow Travellers")
MacRanald and MacTavish didn't know it, but they were half-brothers. Their father was a traveller himself, perhaps a salesman, who had a little fling with the mother of MacTavish around the same time he got his own wife pregnant with Angus.
I don't think either one was ever aware of the other's existence before the death of Angus MacRanald.
This theory of relateeveety is in memory of Angus Lennie, a Scottish actor who died back in September of last year. He is best known for his Cineverse role of the Mole in "The Great Escape" and for playing Shughie McFee in 'Crossroads' in Toobworld. (A character who might also have been the bastard son of the elder MacRanald......)
Good night and may God bless.