Sian Berry, principal speaker for the party, called on the Government to repeal a part of the Serious Organised Crime and Police Act that bans groups and individuals from holding impromptu demonstrations outside Parliament.
Instead, she said, Parliament Square should be pedestrianised and people allowed to campaign without restriction.
Berry told Third Sector: "It is time to scrap the laws restricting protests at Parliament Square as a waste of police time and resources.
"As a zone of free protest, Parliament Square would become a place where democratic protest is positively encouraged, a space made available to anyone who has an issue to raise, with no pre-booking required."
Berry believes that Socpa, which requires groups to apply to the police at least six days in advance if they want to hold a protest, has had a bad effect on small NGOs in particular.
"Many have adapted their tactics and probably don't do protests as much as they did," she said. "Smaller organisations and groups are particularly vulnerable - the smaller you are, the less resources you have to jump through Socpa hoops."
Rosamund McCarthy, a partner at the charity law firm Bates, Wells & Braithwaite, who has been working with groups such as the Sheila McKechnie Foundation to counter the ban on unplanned demonstrations, welcomed the proposal.
"I think that the heart of a democracy should be a place where people are encouraged to express rights and opinions," she said. "Parliament shouldn't be insulated from listening to and hearing people protest. Most of the time, people protest in a good-natured way."