The performer is pictured in Parliament Square, Westminster wearing a 'Blue Eyed Freak' T Shirt. The campaign from Kaleidoscope Trust asks people to imagine "What if it were illegal for you to be you?" The video shows people being persecuted and attacked for things they can do nothing about — having blue eyes or being short.

John Barrowman said:

"Can you imagine what it would be like to wake up one morning to discover that it was suddenly illegal for you to be you? That the law said because you had blue eyes, or were short or because you wrote with your left hand you could go to jail.

If it's hard to picture, just take a look at this short video released today on the internet. There's a guy being beaten up who could so easily be you. Or maybe you could be the woman being subjected to all that verbal abuse.

The images had a really profound impact on me because for millions of people like me who just happen to be gay it's not some grotesque Kafkaesque horror story. It's the every day reality of their lives.

The character I'm best known for — Captain Jack in Torchwood — spends his life fighting every kind of threat to humanity you could think of. That's all fantasy, of course, but this is real. People are being killed and many, many more live in daily fear for their lives. And the threat comes from something that is much harder to fight than fictional aliens — homophobia based on prejudice, hatred and ignorance.

The video has been launched by an inspirational new global LGBT rights charity called the Kaleidoscope Trust. When they gave me the figures for just how many countries still make it a crime to be a gay I could scarcely believe it. No fewer than 78 states around the world criminalise homosexuality. In five of them the maximum penalty is death.

When we demand our rights to complete equality under the law, including the right to marry, we need to remember that for literally millions of gay men and women the right not be beaten up, arrested or even killed would be a massive step forward."

The campaign will launch with the unveiling of the video on Kaleidoscopetrust.com and YouTube on July 4th and has been produced by advertising agency M&C Saatchi for the Kaleidoscope Trust, the only UK charity to campaign exclusively for global LGBT human rights.

John Barrowman said: "I've had a sneak preview of this video and it's powerful stuff. It brings home to people how they would feel if some crazy law made it illegal for them simply to be themselves."

"What if it were illegal for me to want to sing? Or to have an American accent? As it happens, I'm gay. When the Kaleidoscope Trust pointed out to me that it's illegal to be gay in 78 countries around the world, and that in five of them the maximum penalty is death, I was staggered by those figures. People — whether gay or straight - need to wake up to the scale of the injustice that is going on out there."

"We are all human beings and we all deserve the same rights. And that includes the right to love whoever we choose to love."