As this year's Edinburgh Festival celebrates the Scottish political song, Chris Wood asks what makes an anthem inspire allegiance.

Things can only get better" was the message that blared from every radio about the time of Britain's general election in May 1997. The statement is arguably as true today as it was then - but of greater interest than the message was the medium used to convey it. This mantra, like so many other political messages, was sung. If you want to say something memorably, the trick, it seems, is to set it to music.

Such could be the conclusion of a celebration of Scottish political song at the Edinburgh Festival this year. Conceived in association with the Centre for Political Song at Glasgow Caledonian University, a series of concerts running throughout the festival presents songs ranging in time from the 17th century to the present day and espousing causes as diverse as Jacobitism and saving a Glasgow Swimming pool.

As the concerts show, political song is a highly versatile tool and one of its major applications has been to support nationalist movements. The Scots are still basking in the bright dawn of devolution, an event that stirred up the perennial nationalist debate concerning the Scottish national anthem. The song that is sung on football and rugby terraces at international matches is Flower of Scotland , written by Roy Williamson of Scottish folk group The Corries, although God Save the Queen remains the official anthem of the UK. The latter, however, is unacceptable to many people north of the border, not least for a little-known verse that runs:

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"Lord, grant that Marshal Wade, / May by thy mighty aid, / Victory bring. / May he sedition hush / And like a torrent rush, / Rebellious Scots to crush, / God save the King". Marshal Wade was a commander of the forces that opposed the Young Pretender's uprising in 1745. Not very tactful.

However, Flower of Scotland commits the same lapse in good taste by also recalling bad relations between the neighbours, this time at Bannockburn:

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"Flower of Scotland / When will we see / Your like again, / That fought and died for / Your wee bit o' Hill and Glen / And stood against him / Proud Edward's Army, / And sent him homeward / Tae think again."

It is a thorny issue, but Janis McNair of the Centre for Political Song believes it could be resolved by opting for another candidate, A Man's a Man for A' That by Robert Burns. "The socially democratic nature of that song is something that's very important to the new Scottish nation," McNair says.

"There's been a wholesale rejection of God Save the Queen , but it has always been stated by the Scottish Parliament that our desire for devolution and possibly independence is nothing to do with anti-English sentiment." This despite a startlingly sudden allegiance to the Brazilian football team prevalent in Scotland during the recent World Cup.

Burns' poem received the official honour of being sung by Sheena Wellington at the opening of the Scottish Parliament, and certainly has a diplomatic universality to it, even if there are a few words that the English might scratch their heads over. "Is there for honest poverty / That hangs his head and a' that? / The coward slave, we pass him by / We daur be puir for a' that."

These linguistic difficulties are as nothing compared with another candidate, Freedom Come All Ye , by the Scottish poet and composer of folk songs Hamish Henderson, who died earlier this year. It opens: "Roch the wind in the clear days dawin / Blows the cloods heelstre-gowdie ow'r the bay / But there's mair nor a roch wind blawin / Through the great glen o' the warld the day."

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Henderson's song may possess the virtue of confounding the English, but McNair pinpoints a problem. "People want to cherish his memory by adopting that song as the national anthem," she says, "but Henderson would have been horrified at the prospect. He very much viewed it as an international song - to have it used for nationalistic purposes, I think he would be turning in his grave."

The issue of what makes a successful political song is complex, although the goals of the song are clearcut: "to motivate, to inspire, to solidify feeling and unify a group", according to John Powles of the Centre for Political Song. But how to do it? Some songs are defiant and glory in past victories; some opt for a lament for lost freedom (as in Irishman Thomas Moore's tear-stained "The harp that once through Tara's Hall / The soul of music shed / Now hangs as mute on Tara's wall / As if that soul were fled"). Some are jingoistic, some conciliatory; some parochial, some international. Whatever the approach, a song must sink into the public consciousness, and often the ones that do so are not the anthems.

McNair insists: "Songs such as We Shall Not Be Moved and We Shall Overcome from the American civil-rights movement are more important and more easily remembered than many countries' national anthems. They are still known today and sung at local demonstrations. If you ask people to sing their national anthem they start to tail off after the first verse."

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A song's acceptability can be aided if, like We Shall Overcome , it can transcend the context in which it was written. " We Shall Overcome is not associated with one movement or one social group or one aspect of the political spectrum," McNair notes. "It is very important not to be aligned to one movement or period in time."

Nonetheless, certain songs have a local historical significance that renders them exceedingly potent. The national anthem of the world's newest nation, East Timor, was originally used in that capacity during the short life of the Democratic Republic of East Timor, declared by Fretilin forces resisting Portuguese colonial rule in 1975. The song's popularity cannot have been harmed by the death of its author Francisco Borja da Costa in December 1975 on the day East Timor fell to Indonesian forces, who subsequently butchered thousands of East Timorese.

According to McNair, songs were an important part of the resistance struggle waged over the past years. "Song has traditionally provided a voice for a silenced minority," she says. "In East Timor the revolutionary front's encouragement of people to write their own songs supported the whole struggle. It was a very powerful tool."

Song is also a valuable part of the work of the Free Tibet Campaign. A collection of songs was clandestinely recorded in prison by 14 Tibetan nuns jailed for attending a pro-independence rally. On learning of the recordings, the Chinese authorities increased the jail terms, but the songs are nevertheless now in the public domain and sales of CDs go towards supporting the campaign to liberate Tibet from Chinese rule.

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So whether the oppressor is Glasgow City Council - as in the case of the protestors against the closure of Govanhill swimming pool who, with a nod towards Burns, have recorded a song called We'll Swim Again for All That - or the Chinese government, political song is alive and well and being used to express disapproval of bureaucratic incompetence as well as to foster nationalist movements. As McNair says: "Political song has existed as long as songs have been written. There's a continuity. It is not inconsistent to perform Jacobite songs in the same programme as songs about the chief executive of Enron."