By Jemima Kelly

GLASTONBURY, England (Reuters) - Revelers at Glastonbury Festival emerged from their tents in shock on Friday morning at the news Britain had voted to leave the European Union and the prime minister would be resigning.

Organizers of the Britain's best-known music and arts festival, held on a dairy farm in southwest England, opted firmly for the "Remain" camp ahead of Thursday's referendum, erecting a large "In" sign outside the publicity tent.

Most festival-goers had also seemed to support the campaign to keep Britain in the EU, some trudging through Glastonbury's muddy fields draped with blue and yellow-starred European flags, and others flying the flags over their tents.

Though the referendum did not appear to be at the forefront of most revelers' minds on Thursday night, as parties ran until the early hours, the mood seemed more somber on Friday as the news of the ballot result spread.

Glastonbury-goer Tim Bienias, the 61-year-old son of a Polish immigrant, had voted to remain on his way to the festival on Thursday.

"I've just heard my daughters and my wife crying on the phone, so I feel pretty upset myself," he said.

"I think there's going to be an awful lot of people that are going to see a few years down the road that this is an extraordinarily bad decision. Ultimately, I don't even think we should have been given a referendum."

Those who arrived at Glastonbury before Thursday had to have submitted their vote by post or appointed a proxy if they wanted to take part in the referendum, as the Electoral Commission did not allow polling stations inside the festival.

TOO YOUNG TO VOTE

Some youngsters at "Glasto" expressed frustration that only those over 18 could vote.

"My opinion is completely invalid, according to the government, because of my age," said 17-year-old Lauren Haycock. Most young voters opted to remain in the EU on Thursday.

Some at Glastonbury - an apparent minority - were pleased with the outcome of the referendum.

"I'm of an age where I remember us before we went into the EU," said Andy Dunn, from Wolverhampton.

"I didn't want us going in in the first place, but I remember Great British manufacturing and I think we can do it again ... We have so much going for us that we can stand on our own quite comfortably."

Glastonbury runs until June 26, with Adele and Coldplay among the headline acts and Labour leader Jeremy Corbyn due to speak.

(Reporting by Jemima Kelly; editing by Andrew Roche)