Marchers in London gathered outside British Music House, home to several major rights holders
Thousands of people have taken part in co-ordinated protests across Europe in opposition to a controversial anti-piracy agreement.
Significant marches were held in Germany, Poland and the Netherlands against the Anti-Counterfeiting Trade Agreement (Acta).
Around 200 protesters gathered in central London outside the offices of rights holder representative groups.
Demonstrators argued that Acta will limit freedom of speech online.
However the agreement's supporters insist it will not alter existing laws, and will instead provide protection for content creators in the face of increasing levels of online piracy.
The treaty has to date been signed by 22 EU members, including the UK, but has yet to be ratified by the European Parliament. A debate is due to take place in June.
On Friday, Germany delayed signing the agreement in order to, a spokesman said, "give us time to carry out further discussions".
Saturday's London demonstration was supported by the Open Rights Group, a vocal opponent to the treaty. The group's executive director, Jim Killock, argued that Germany's stance shows Acta negotiations were carried out "in secret" by EU "bureaucrats".
What is Acta?
The Anti-Counterfeiting Trade Agreement is an international treaty aiming to standardise copyright protection measures.
It seeks to curb trade of counterfeited physical goods, including copyrighted material online.
Preventative measures include possible imprisonment and fines.
Critics argue that it will stifle freedom of expression on the internet, and it has been likened to the controversial Stop Online Piracy Act (Sopa).
Acta has been signed by 22 EU members, including the UK, but is yet to be ratified by the European Parliament.
"Three member states in Europe are now looking like they don't want to sign," he told the BBC.
"That shows that politicians are only really starting to look at this now. All of a sudden, the whole thing is breaking down."
Poland, the Czech Republic and Slovakia have already delayed the process after significant pressure from mostly young people.
"The point today is to say Acta is undemocratic," Mr Killock added.
"It's lacked scrutiny, it's setting up dangerous new pressures to censor the internet to remove users and put pressure on [Internet Service Providers] to start policing for copyright."
More demonstrations were held in other UK cities, including Edinburgh and Glasgow.
The anti-Acta movement has also been widely adopted by members of the Anonymous activist collective, which has claimed responsibility for putting high-profile government websites out of action, including that of the Polish prime minister.
Speaking at the London protest Loz Kaye, leader of the Pirate Party UK, dismissed worries that aligning closely with Anonymous - some of whose members have carried out various illegal activities online - was harmful to their cause.
"What we've seen is a whole wave of people coming out on the streets right across Europe," he told the BBC.
The BBC contacted several key rights holder representatives prior to the demonstration - all of which declined to comment.
The UK's Intellectual Property Office has maintained that Acta "should not" mean new laws relating to internet use.
In a statement, Baroness Wilcox, parliamentary under-secretary for Business, Innovation and Skills, told the BBC: "It was important for the UK to be a signatory of Acta as it will set an international standard for tackling large-scale infringements of [intellectual property rights], through the creation of common enforcement standards and more effective international cooperation.
"During the negotiations, we continually pushed for greater transparency as we believed that this would have led to a better understanding of the agreement by the public."