From: Steve Shaw - PM
Date: 06 Apr 11 - 05:03 AM
Modern usage: any Scot who loses something is Scottish. Any Scot who wins something is British. Examples:
"The British women's curling team won gold in the 2002 Winter Olympics."
"The Scot Andy Murray once more failed in his Wimbledon bid."
Easy!

A little unfair that. While I recognise the scenarion you describe , used by English commentators, the examples you give don't fit.
The 2002 curling team were competeing for "Team GB" and so should be described as British. Andy Murray competes as an individual, and so can be described by any suitable term.

Worse is when Andy Murray is described as British if he wins & Scottish if he doesn't!