Baroness Tonge has had her party membership suspended by the Liberal Democrats after she hosted an event at the House of Lords at which audience members compared Israel to Daesh terrorists and suggested Jews were to blame for the Holocaust.
The controversial peer was told she would be subject to a party investigation last Thursday after the Board of Deputies met Tim Farron, Lib Dem leader, and urged him to act.
But Baroness Tonge attempted to nullify the suspension by immediately resigning her membership.
Two days earlier she had hosted a session organised by the Palestine Return Centre session launching what the group calls the Balfour Apology Campaign, ahead of the centenary of the Balfour Declaration next year.
In video clips of the event posted online, one man in the audience was shown describing Zionism as a "perversion of Judaism", and implying Rabbi Stephen Wise, a leading figure in the United States in the 1930s, had provoked Hitler into murdering six million Jews in the Shoah.
The man - reportedly from the anti-Zionist strictly Orthodox Neturei Karta sect - claimed Hitler was "pushed over the edge" by the rabbi's comments, and went on to talk about boycotts.
Baroness Tonge responded: "Thank you very much. I think it's very important that the word boycott has come up. The BDS, the campaign to boycott Israeli goods and services, and divestment from Israel, most of us think is very, very important indeed."
Another speaker was shown announcing, to applause: "If anybody is antisemitic, it's the Israelis themselves."
Writing on Facebook after quitting the Lib Dems, Baroness Tonge said: "One member of the audience made a 'rant' against Israel quoting some very confused history which I confess I did not hear or understand!
"I then called the next member of the audience and moved on. The contribution was ignored by the audience after a few claps of relief! Apparently this is my sin!
"I am at last free of being told what I must and must not say on the issue of Palestine, lest it offends the Israel lobby here, who like to control us, as they do in the USA.
"They are trying to destroy the Labour Party with spurious accusations of antisemitism and now they have set their sights on the Lib Dems. I have never been antisemitic, and never will be."
Stephen Sizer, the controversial Church of England vicar, was reprimanded by the Bishop of Guildford following the session.
Rev Sizer breached the terms of an agreement he had made with bishops promising not to engage in anti-Israel activity by attending the event and posting about it on Facebook.
The PRC said: "We don't tolerate any form of antisemitism nor Holocaust denial statements."