cool point Alan, someone born in Scotland in the eyes of the law isnt a Scot , they are British, so I think that a Scot is someone whos alligience is to Scotland, even being born in Scotland doesnt make you a Scot, prime minister Tony Blair is a good exmple he was born in Edinburgh but he does everything to hide his celtic roots and even had elocoution lessons to get that "neutral" accent to widen his voter appeal, plus the supports the English football team. clearly hes not a Scot.
HM the late queen mother was the daughter of the Earl of Strathmore, she was born in London but is regarded as a Scot, and is still held in esteem in Scotland. There is no true test you can take for being a Scot, being born here helps your case, having and accent helps too but I know many asian and Chinese shop keepers who have Scots accents but are proud to be asian or chinese despite the accent ! .
to play for the Scottish football team you can go back to your Grandparents being born here, several scottish footballing "greats" were not born here.
My own view is that you need some kind of connection, family or an interest, in all things Scottish. Scotlands always thrived on immigrants, you get as many Irish names here as scots, and lets not forget that William Wallace was of Welsh descent !