An illegal alternative Glastonbury festival, which organisers claim will attract crowds of 20,000, could be stopped by legal action.

The organisers of the event claim thousands of people without tickets for Glastonbury, will flock to the alternative concert.

But council officials want to stop the fringe event, due to take place on the same weekend as the main festival on 29 and 30 June.

The organisers have no licence to hold the concert and council officers said they would seek a court injunction.

Organisers have designed a web site

A 12-feet high "super-fence", costing �1m, has been put up around the main festival this year to prevent gatecrashers.

Craig McFarlane, organiser of the alternative festival, said that means there will be a ready-made crowd for a second concert.

"There is going to be a lot of people coming to the area, to the festival, without tickets but who are adamant about getting in.

"We would like to put something on for those people and hopefully it will ease tension for people around the festival as well," he said.

'Not illegal'

The organisers said the venue for the alternative event would not be revealed until the day of the concert.

Charlie Barley, another organiser, said: "I don't think it should be illegal.

"It's not illegal for people to be here."

When the main festival was held in 2000, on farmland near the village of Pilton, Somerset, crowds of more than 200,000 attended.

Police estimated half the audience did not have tickets.

'Prevent disturbance'

The 100,000 tickets for this year's main event have all been sold.

Suzanne McCutcheon, of Mendip District Council, said action would be taken to prevent an alternative concert taking place.

"We would propose that an injunction be taken out to prevent access to the land," she said.

"If they did gain access we would be looking for assistance from the police to move equipment and prevent any disturbance to local residents."