LONDON (AFP) - If Scotland chooses independence on Thursday, it is not only the politics of the United Kingdom that will be profoundly changed, but also potentially its iconic "Union Jack" flag.

Designed more than 200 years ago, the flag combines the colours of the three patron saints of England, Northern Ireland and Scotland. In the event of a "Yes" vote on Thursday, some believe the white diagonal cross and blue background of the Scotland could disappear. A new design would then be needed, raising numerous issues, such as whether the green of the Welsh flag, which is currently absent, should be added.

According to an online survey by the Flag Institute (FI), the British heraldry association, 65 per cent of the general public believe that the flag should change in the event of a "Yes" vote. But the most difficult issue would be deciding what to change, warned Graham Bartram of the FI, because "there are lot of opinions".

Prime Minister David Cameron is refusing to entertain the possibility of a "Yes" vote, and a spokesman from his Downing Street office said that there was "no plan about the flag".

The Flag Institute has received many proposals for a new flag, some far-fetched, and believes that the government "will not try to impose anything", and will instead let the people decide on a new design, probably by vote.

Constitutional experts question the need to change the flag, pointing out that it represents a union of crowns, and not nations. Since Scotland's nationalists have promised to keep Queen Elizabeth II as head of state, it seems that one of the United Kingdom's most famous exports may live to fly another day.

The FI's Bartram also questioned the need to change the flag, whatever the result. "It's the most recognised flag in the world... why take it away?" he asked.

Indeed, the Union Jack has become more than a flag, and is now an iconic symbol available on every conceivable product, from postcards to teacups, ashtrays and clothes.

Bartram put the flag's ubiquity down to its "very unique design" and association with the British Navy, which "took the flag everywhere" when it ruled the waves.

It is believed the flag takes its surname from the small flags, called Jacks, that used to fly at the front of the Navy's boats.