Fathers 4 Justice have run a high-profile, often controversial, campaign for improved rights for men denied access to their children.
The group's protesters have hurled packages of flour at former Prime Minister Tony Blair in the Commons and climbed all sorts of buildings dressed as superheroes.
The group was briefly disbanded in January 2006 following allegations that people linked to the group plotted to kidnap Tony Blair's youngest son, Leo.
But the organisation was reformed the following May, an event it marked by disrupting a live broadcast of the National Lottery draw.
Dyed flour was thrown at Tony Blair in the House of Commons
Matt O'Connor, a father-of-two, founded the group after a difficult divorce left him struggling to maintain contact with his children - although the problem had been resolved by the time Fathers 4 Justice was up and running.
"So many people have lost contact with their children through the courts, it was inevitable something like Fathers 4 Justice was going to emerge," he has said.
The group's early meetings with the government achieved little success, prompting it to launch in 2004 a national campaign of civil disruption.
Fathers 4 Justice admitted protesters would be running the risk of imprisonment but said they had "exhausted every possible avenue" and the tactics were a "last resort".
"We are a bunch of guys who are going to be making some pretty scary sacrifices," said Mr O'Connor at the time.
"It comes down to the simple fact that we face a Herculean struggle. The politicians are not dealing with this with the degree of urgency this matter deserves."
Among numerous demonstrations on cranes, key roads, bridges, public buildings and monuments, the most high-profile protests included:
- Two men throwing packages of flour dyed purple at Tony Blair during prime minister's questions in May 2004
- A man dressed as Spiderman scaling the London Eye and staging an 18-hour protest that closed the attraction in September 2004
- In the same month, a campaigner dressed as Batman staging a five-hour protest on a ledge by the Buckingham Palace balcony
- Three men dressed as superheroes scaling a Foreign Office balcony overlooking Downing Street in March 2005.
The group condemned the plot by fringe members to kidnap the prime minister's son, over which Mr O'Connor said he was made "very angry and upset", and it temporarily disbanded in the wake of the furore over the incident.
When the group reformed in May 2006, Mr O'Connor was said to have taken a more behind-the-scenes role as a media adviser.
He has since gone on to stand for Mayor of London as the candidate of the English Democrats party.
In March 2007, the organisation staged a demonstration in York Minister - with protesters dressed as monks and nuns - which it said marked the start of a renewed national campaign.
Fathers 4 Justice wants parents and grandparents to be given "a legal right to see their children and grandchildren".
"The law says you have no legal right to see your children - only a right to apply to a court to see them - but you have a legal obligation to pay for them," Mr O'Connor has said.
Demos have promoted the campaign but also drawn criticism
"Fathers are forced to support children even when mothers are not being forced to allow those fathers access."
He argues that family court-issued contact orders intended to ensure access for the parent not living with their children are worthless because they are not enforced.
The government admits that the enforcement of contact orders is "an issue" that needs to be addressed.
But Fathers 4 Justice's actions have attracted criticism.
Tony Coe, president of the Equal Parenting Council, recognised the "real tragedy and frustration" behind the 2004 Buckingham Palace protest.
But he added: "We don't think that this kind of unlawful action helps, in fact it alienates the very people that we are trying to persuade."
Then home secretary David Blunkett added that the group had done its "very reasonable" cause a disservice by acting in a "foolish and silly" way.
When a protester dressed as Spiderman climbed a crane on Tower Bridge, London, in November 2004, city Mayor Ken Livingstone said the stunt demonstrated why "some men should not have access to their children".