A group of Sussex animal rights protesters have been stopped from streaking through the streets in protest at Spain's Running of the Bulls event.

By day they have professional jobs but in the heat of the midday sun, they prepared to bare all in the city of Pamplona.

Some simply wore plastic horns or fake bull's heads to get their animal cruelty message across. Others kept their underwear on.

They were happy for the crowds and photographers to stand and watch as they made their protest against one of Spain's most famous traditions.

But it was not to be. Police turned out in force to stop the race, blocking the road on both sides.

Protesters included a sales manager at Gatwick Airport, a web site designer, a care worker from Brighton and a former Brighton University student.

They were forced to stand or pace around the enclosed area chanting: "Stop the bull run" in Spanish, English, and German, while waving placards.

About 40 people spent 22 hours on a coach from Britain to join scores of others from across Europe to streak at the event, dubbed as The Running of the Nudes or the Human Race.

Arriving in Pamplona, they made their way to the city's corrals, where the bulls traditionally start their stampede as part of the ancient San Fermin festival.

Protesters, including Spaniards, Italians, Portuguese, Germans, Belgians, and New Zealanders chanted: "Shame on Spain" as they prepared to disrobe for the stunt.

Sean Gifford, director of European campaigns for US-based group People for the Ethical Treatment of Animals (PETA), said it was ridiculous police had banned people from running through the streets.

He said: "It's not as if they could be carrying any concealed weapons."

Sean said bullfighting was a hideous spectacle which had been outlawed in half a dozen Spanish cities.

The aim of their stunt was to show tourists there is an alternative to the traditional race.

He said: "In the Running of the Bulls you have terrified animals slipping and sliding along the cobbled stone streets, many of them suffering broken bones. At the end of the stampede, a gruesome death in the bullfighting ring awaits them.

"Forty thousand bulls are slaughtered in Spanish bullrings every year in the most horrific of ways. This tradition needs to end.

"We can't even go into the town centre to show the mayor our views. We want to run through the streets naked and show there can be an alternative festival.

"People may try to justify the Running of the Bulls and bullfighting by saying it is tradition but that is no argument.

"Years ago in Spain people used to throw goats headfirst from buildings. Now that tradition is banned because people like us keep returning and protesting. I hope we can all come back year after year until we get this tradition closed down."

In 2002 about 20 people went to Spain for the PETA protest. This year some 200 took part, with about 40 stripping completely.

Adrian Cooper, of Kemp Town, travelled from Brighton for the protest.

The 27-year-old web designer, who wore just a red necktie and sandals on the day, said: "Bullfighting and the Running of the Bulls is killing for killing's sake, with a whole load of cruelty thrown on top.

"I think all blood sports are disgusting. It's worth baring all if it brings attention to the plight of animal suffering."

Adrian said he was disappointed at not being able to do the race but would try again next year.

He said: "It's an interesting experience and I don't regret taking my clothes off - it felt great. We managed to make the protest anyway and a couple of hundred people watched from up on the walls. We certainly got their attention."

The protesters stripped the day before the start of the San Fermin festival, which kicks off a week of celebrations made famous by Ernest Hemingway in his novel The Sun Also Rises.

Each morning from the second day of the festival, bulls are released into the older area of Pamplona and run 2,707ft to the bullring, where they are fought.

Hundreds of daredevil spectators run in front of the bulls and are often injured. Since 1900, 13 people have been killed.

Another naked protester at Saturday's demo was former Brighton University student Alan Donahoe.

Alan, 27, who is a vegan and works at a London hospital, said: "I'm glad I took my clothes off but I still feel I could have done a bit more - maybe shouted a bit louder.

"I'm not worried about people seeing pictures of me in the buff, except maybe my work mates. I'll be back next year."

Barb Trenholm, of Wilbury Gardens, Hove, took time off from her job working with autistic adults and children in Brighton for the event.

The 51-year-old, who has been an animal rights campaigner for more than 20 years and took part in protests against live exports at Shoreham in the mid-Nineties, opted to wear white shorts and T-shirt.

She said: "I didn't really know what to expect, especially as I didn't know anyone before I got on the coach.

"I'm so pleased I made the effort and we made a statement.

"It was a really good European turnout but the police had a problem with the nudity."

The protest also attracted people from outside Europe, including New Zealanders Lisa Julian, 22, and Rose Mein, 21, who are living in London. They described the protest as an enlightening experience.

They were among people in the front row of protesters shouting into the faces of police.

Officers formed a line and pushed back anyone who attempted to break through.

No one was hurt but one nude demonstrator, who would only be identified as Ralph, was hauled off by police. He was soon released.

After about 50 minutes, the demonstrators reluctantly put on their clothes and police let them pass into the city.

Gary Boyce, 55, said: "I feel as strongly about bullfighting as I do about fox hunting.

"I'll be back next year, although I reserve judgement on whether I'll take my pants off."