More than 1,000 supporters turned out to lobby MPs to drop key measures in the draft version of new mental health legislation which it is claimed could turn "doctors into jailers".
Supporters of the Mental Health Alliance campaign sought meetings with their MPs via the "green card" system of drop-in appointments at the House of Commons.
As part of a campaign launched in 1999, the alliance's latest protest included holding a forum in nearby Church House where a selection of key figures spoke.
Alliance chair Paul Farmer described the draft bill as "unworkable" and "fundamentally flawed". "We urge the Government to seize this chance to pass mental health legislation fit for the 21st century before it's too late," he said.
The alliance believes its opposition was "unified and focused" and that there would be a "detailed line-by-line lobbying campaign".