The Severn Bridge was shut for several hours during the protestFour fathers' rights campaigners who closed the M4 after scaling a gantry on the Severn Bridge have each been given a conditional discharge by a court.
The three men and one woman, members of the Fathers 4 Justice group, were dressed as Santa Claus for the protest.
The M4 was closed both ways during the five-hour protest on 28 November, 2004.
Elaine Risk, and Michael Downes, from Manchester, Jolly Stanesby, of Devon, and Darryl Westell, of Nottingham, admitted causing a public nuisance.
No evidence was offered at Newport Crown Court on a further charge of causing a danger to other road users by interfering with traffic equipment.
I can't encourage protest, but the reality is that there is a long standing history of respectful and peaceful protest in this country
Judge Jonathan Durham Hall QC
The court heard that the M4 between England and Wales was closed for several hours while the demonstration was held.
Martyn Kelly, prosecuting, said: "On November 28, the defendants, as part of their campaign, climbed onto a gantry.
"The nuisance is that the sergeant who had to take an operational decision at that stage, felt quite clearly there was a danger.
"As a result of that, he called for the M4 to be closed. That meant in both directions because everything had to go up the old A48, over the old bridge."
Piers Marquis, defending Risk, 45, and Downes, 43, said his clients' actions were part of a legitimate protest.
He added: "This was clearly a protest and demonstration that was raising a legitimate point of public interest.
"It was peaceful, it was humorous, and was without malice or ill intent."
Huw Wallace, defending Stanesby 39, and Westell, 23, said: "There was no accident as a result of what they did.
"It was a peaceful, humorous protest and they came down, not willingly, but when the police came up for them.
"They had legitimate grievances and they brought it to the public's attention. There was no intent to cause the disruption that occurred."
Judge Jonathan Durham Hall QC told the four, who were wearing Fathers 4 Justice t-shirts in the dock: "I hope I'm sensible enough to realise this is not the run-of-the-mill criminal case.
"I don't think for one minute that any of you were acting in malice.
"I can't encourage protest - you appreciate that - but the reality is
that there is a long standing history of respectful and peaceful protest in this country."
In addition to a 12-month conditional discharge imposed on each of the four, Judge Durham Hall also ordered them to pay £50 costs each.
Outside the court, Jolly Stanesby said: "If the laws were a bit fairer, we wouldn't have done it. I don't think we should have been here in the first place."