I'd say potato scones are a scone mix with added potato
Farls are a soda bread mix with potato

Or so I think, if anyone wants to correct, feel free.
( Spider Fucking Riviera got stiches for a knife wound for the first time, Sun 7 Jun 2009, 10:08, archived)

As far as I was aware (and from the recipe I have)
Both potato farls and potato scones are basically mashed potato with butter, flour and salt. Then fried.
( Pickle Fairy is clumsily dancing away this fear, Sun 7 Jun 2009, 10:11, archived)

Stand corrected then.
You're still wrong down below though.
( Spider Fucking Riviera got stiches for a knife wound for the first time, Sun 7 Jun 2009, 10:14, archived)