Labour’s Lisa Forbes has won the Peterborough by-election despite her suitability being questioned after it was revealed she had liked anti-Semitic social media posts.

The Labour candidate had previously liked a post that said Theresa May had a “Zionist slave masters agenda”. She also commented on another post that claimed ISIS was was created by the CIA and Mossad, by writing: “I have enjoyed reading this thread so much.”

Forbes  pledged to go on “anti-Semitism training” after the revelations came to light days before Thursday[s by-election.

Labour MP Jess Phillips said, “I cannot be (as) gleeful or proud as I’d want to be because of how it shows that antisemitism is becoming normal in the party”.

“Lisa ignored and endorsed antisemitic things, I’ll take her explanation and apology at face value and look forward to her proving, as others have, that actions not excuses alone can heal.

“But with every case the parties values chip away and our ability to stand up against hate erodes.”

Forbes apologised for her social media activity, which was uncovered by freelance reporter Iggy Ostanin, who shared his findings last Friday. But Jewish groups questioned her suitability as an MP, ahead of the by-election.

In a joint statement, the Board of Deputies of British Jews, Jewish Leadership Council, and Community Security Trust, said her social media activity “brings into question her suitability for public office”.

“We are fed up hearing that Labour opposes antisemitism while repeatedly hearing excuses that its members accidentally missed the racism that was staring them in the face,” the statement read. “Unless Labour disowns Lisa Forbes as a candidate, it will only confirm the party’s shameful descent into the racist mess for which they are now being investigated by the Equality and Human Rights Commission.”

Following immediate criticism, Forbes “wholeheartedly apologised” for failing to condemn the posts and pledged to undergo antisemitism training.

“Standing up against hatred towards one group of people must never be allowed to become hatred of another,” she said. “Regardless of whether I am elected, I will deepen my understanding of antisemitism, so I can act as an ally, challenging antisemitism wherever it occurs.”

After the results, Journalist Melanie Phillips commented in her blog that “it shows that the Labour Party will continue to turn a blind eye to the antisemitism rampant among its supporters. But we know this already, don’t we. The Equality and Human Rights Commission has launched a formal inquiry into the huge number of complaints of antisemitism by its members and its failure to address the problem.”

She continues, “Even worse, however, than the Labour party’s indifference towards or connivance with the Jewish-conspiracy ravings in its ranks is the attitude of the British public. For the by-election result shows that the stench of antisemitism is failing to repel the voters. Either they don’t care or, worse, they may actually be sympathetic – perhaps because they don’t like what they perceive as people ganging up on someone. That’s a very British thing.”

“The answer is probably that, in addition to those who actually do believe this poison, there are many who don’t notice it to be poison. And that’s because too many don’t think antisemitism is unambiguously bad.”