Just a point of pedantry, bayliss, the flag you are talking about is not the George Cross flag. It is the flag of Saint George, the patron saint of England. It depicts a red cross (known as the cross of Saint George).
The George Cross (which I do not believe has an associated flag) is the highest civil decoration of the United Kingdom, the civilian equivalent of the Victoria Cross (VC) and the highest gallantry award for civilians.
Saint George’s Day is on April 23rd, but strangely I never see the flag flying then or on any other appropriate occasion. I only seem to see it when the English football team is involved in some sort of competition.