Deputy Prime Minister Nick Clegg suffered a stinging defeat today when Liberal Democrat activists overwhelmingly rejected the coalition's secret courts legislation.
Just hours before Mr Clegg was set to close the Lib Dem spring conference in Brighton with a keynote speech, delegates ordered their MPs and peers to oppose the plans as they were contrary to "core" Lib Dem values.
Lawyer Jo Shaw announced in the hall that she was resigning her membership in protest, joining human rights barrister Dinah Rose QC, who represented Guantanamo detainee Binyam Mohamed in his case against the intelligence services.
The Justice and Security Bill was passed its third reading in the Commons last week, despite a rebellion from some Tories and Lib Dem MPs and continuing opposition from civil rights campaigners.
Members ignored pleas from deputy leader Simon Hughes and Justice Minister Lord McNally to pass an emergency motion on secret courts.
Ms Shaw said the leadership had "abandoned liberal values for the privileges of power."
Ms Rose added that her decision to resign had not been "taken lightly."
She said: "The right to a fair hearing and the right to open justice are among the most fundamental of all our basic constitutional rights.
"I just cannot see what purpose is served by the party, if it is prepared to support the Bill. I have therefore decided, with great regret, to resign my party membership."
Campaign group Liberty director Shami Chakrabarti said: "Many Lib Dems are rightly horrified by the Secret Courts Bill and astonished that the party which once made civil liberties its unique selling point is now exchanging Mill for Kafka."