What would the union jack look like if Scotland votes for independence?

Scotland's referendum on independence is now just over 10 months away, but the question of what might happen to the union jack has been largely overlooked. An association of flag experts, or vexillologists, has created a set of designs it hopes will encourage a discussion.

Some 400 years ago when the crowns of England and Scotland were united, an argument raged about how the blue field and white saltire of St Andrew could be combined with the red cross of St George.

The Scots were eager that their flag should be laid on top of the English banner, but of course the English thought it should be the other way around. It took a Royal proclamation to determine that the English flag should take precedence.

Now, the prospect of Scotland leaving the United Kingdom throws open the question again. It's already been suggested by the College of Arms that with the Queen still head of state of an independent Scotland there would be no need for a redesign. But there is still the possibility of renewed debate.

Charles Ashburner, chief executive of the Flag Institute - a charity that offers advice and guidance about flags and their usage - polled the organisation's members, asking what new designs might be appropriate for a post-independence UK.

While the institute takes no view on whether the flag should be altered - indeed Ashburner suggests that most of its members would oppose a change - it is showcasing a range of alternatives, from institute members and ordinary people, aimed at starting a conversation.

Wales is not currently represented in the union jack because it was part of the English kingdom when the flag was designed. "That will be the obvious first argument: 'If Scotland's coming out then surely Wales must go in'," says Ashburner.

The first design (at the top of this piece) strips out the blue field of the Scottish flag, replacing it with black, and sees the white bands turn a shade of yellow - intended to honour the flag of Wales' patron saint, St David (a yellow cross on a black field).

The second (above) seeks to address the same issue, but by borrowing elements of Wales' current national flag - the field of green and white that lies behind its red dragon.

The third (above) is a more modern interpretation of the design, including the colours of St David's flag and retaining the Scottish blue - to reflect the fact that Scotland would continue to share the British monarchy.

Using the same principle, the fourth removes the white of St Andrew's saltire and imposes a crown and Royal Standard - including England's three lions, the red Scottish lion and the harp, a national symbol of Wales as well as Ireland.

The fifth design (above) removes the Scottish elements from the flag entirely, and adds the Royal Coat of Arms, surrounded by a garland of items symbolic of the Commonwealth nations.

Any suggestions for altering the flag would be complicated by the issue of legality, which is uniquely difficult in the UK. "There's an ambiguous wavy line between statute and royal prerogative," says Malcolm Farrow, president of the Flag Institute.

Unlike most countries, there has never been a flag act in the UK, and so the question of jurisdiction and ownership is a grey area.

Buckingham Palace says the issue is one for the Department for Culture, Media and Sport, which in turn says that the Cabinet Office is responsible for any constitutional issues regarding the flag. The Cabinet Office says that since the issue hasn't been raised for hundreds of years, no guidance is currently in place.

Another organisation that may have some say - the College of Arms - says that the flag is determined by the crown, and was confirmed by an order of the Privy Council in 1800.

Andrew Rosindell, who chairs the All Party Parliamentary Group on Flags and Heraldry, agrees that the matter is unclear. "There is no official legal protocol on flags, to the extent that you can't even say that the union jack is the flag of the United Kingdom."

In 2008 he introduced a Private Member's Bill which attempted to formalise the union jack, but it did not become law. He argues that should Scotland vote for independence, there would be no need to change the flag, however.

"It was created at the time of the union of the crowns," he says - as opposed to full political union, which did not happen for another 100 years. Since the movement for Scottish independence proposes to retain the British monarchy, redefining the flag in the event of a Yes vote would not make sense, says Rosindell.

Farrow agrees, and sees more reasons not to tamper with the flag as it stands. It would open up a political can of worms and and "completely over-ride all the important things which the governments will need to do", he says.

There is no official flag of Northern Ireland, so it would be difficult to represent it on an equal footing. The saltire of St Patrick - the diagonal red cross on the union jack - was incorporated into the design in 1801 to represent the whole of Ireland, and not altered with the creation of the Irish Free State in 1922. "It's such a difficult issue that no-one has grasped that nettle," says Farrow.

Not only that, a number of foreign flags feature a miniature union jack imposed on to their own, from Australia and New Zealand to Fiji and the US state of Hawaii.

"To change our flag would cost millions of pounds," says Farrow - in his view a sum that would be wasted. It would also be likely to prove unpopular with many millions of people.

Despite the objections, the question will continue to be posed, however.

James Hallwood, associate director at The Constitution Society - an organisation that promotes public understanding of the British constitution - says the issue is frequently raised. "One of the most common questions I'm asked isn't about monetary or political independence, it's about what will happen to the flag."

He notes its versatility, and the fact that it is not simply perceived as a symbol of patriotism. "People enjoy the kitsch factor. It can also be used in a tongue-in-cheek way as well," he says.

Ashburner thinks that the establishment will be likely to oppose any change, but public opinion will prompt at least a serious debate on the issue.

"It will be difficult for the country to go through the process of shedding Scotland and subsequently carry on with the same flag that existed before."

He agrees with Hallwood on the strength of the flag, and reflects a common view in praising its layout as an entity in itself. "As it stands it is the best flag design in the world and it would be heartbreaking to see it change," he says.

"But it shouldn't stay the same because nobody is brave enough to think about changing it."

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Readers sent in their own designs. Here is a selection.