By Louisa Lim BBC Beijing

Diao Chunlei sweats as he puffs into his tuba under the hot summer sun during rehearsals before leaving China for Scotland.

Musicians and dancers of the PLA rehearse before leaving Beijing

As a member of the military band of the PLA, he's been practising for their 10-minute performance in the Edinburgh Tattoo for the past three months.

As a fan of U2, Enya and the Beatles, Mr Diao, 33, was thrilled to hear he'd be getting closer to his musical heroes.

As an ardent tuba player, he's also looking forward to finding out what's new in the world of military marching bands.

"We were all very excited to get this rare opportunity to display our skills," he says.

"The Edinburgh Tattoo is so famous internationally, we can learn the latest trends in brass instruments, performance methods and musical line-ups. It's a great opportunity to study."

But as they twirl their flags and blow their horns, the band members know they're marching into a storm of controversy.

Human rights groups are fiercely opposed to their presence and have already staged a protest in Edinburgh.

Martial law

Anne Callaghan, from the Free Tibet Campaign, explains their objections.

"The problem is this year is the 15th anniversary of events in Tiananmen Square and also the 15th anniversary of imposition of martial law in Tibet.

"The Edinburgh Military Tattoo provides a worldwide platform for the PLA to give a different worldview of itself. It is still a force of repression and occupation in Tibet and it is still a force of repression in China itself."

You're only seeing one side of the story, not the whole truth Diao Chunlei

Fifteen years have passed since the Chinese army opened fire on unarmed students in and around Tiananmen Square. It's estimated that hundreds of people died, though no-one knows the exact figure.

But for tuba player Mr Diao it was simply a case of soldiers following orders. He accuses the west of having a simplistic view of the Chinese army.

"You're not seeing the whole picture. In 1998 when there were massive floods, the army was in the frontline of the rescue efforts. You're so prejudiced. You're only seeing one side of the story, not the whole truth."

Like the other band members, he's only had three months of military training in the 19 years he's been in the army.

'Musicians, not soldiers'

Brigadier Gordon Kerr, the British defence attach� in Beijing, says: "They're not soldiers as such, although they are in uniform."

He sees the controversy as a song and dance about a song and dance.

"As far as I'm concerned, we've been engaging with the PLA in a wide variety of activities in the six years that I've been here. This to me seems the least controversial part of our engagement."

That's the line the band members also take. Bandmaster and conductor Yu Hai says they have been the subject of protests before, when visiting Germany and Finland, but he feels these demonstrations are misplaced.

Bands from all over the world amass at the event in Scotland

"I don't care how other people see us, or what protestors feel," says Yu Hai. "As a musician for the PLA, our task is to participate in exchanges and to study. That's why [the organisers of the Edinburgh Tattoo] asked us to attend.

"They don't want us to make a political statement. They asked us for our music."

Nonetheless the musicians realise they are playing a political role as the representatives of Chinese military might overseas. But they're unwilling to be caught up in political discussions.

When asked about the army's role in the Chinese occupation of Tibet and the brutal suppression of students in Tiananmen square, tuba player Mr Diao replies: "These are all political problems.

"We want to use our beautiful performances and music to exchange with the English people.

"We want to serve as a window, a representative to allow the people of the world to understand China."

The band members are hoping their music will help bridge the gulf between them and their critics.

They may not realise just how big that gulf is.