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Several groups came together to organise the “solidarity rally”, including the Board of Deputies of British Jews.
Many people in the crowd held signs that said “release the hostages” and chanted “bring them home”.
Others carried Israeli flags and placards showing the faces of those taken hostage.
Family members of those taken hostage spoke at the rally, as the Chief Rabbi, Sir Ephraim Mirvis, thanked the king, the Prince of Wales and cross-party political leaders for their support after Hamas’s attack.
“It’s at a time such as this that we discover who our true friends are,” Rabbi Mirvis said.
“It’s at a time such as this that words do matter and to all our friends from whom so far we haven’t heard a single word, your silence is deafening. Words do matter.
“Sometimes we hear reference to both sides or the two sides, but we ourselves know there are indeed two sides. One is good and the other is evil.
"Israel uses her forces in order to protect her citizens while Hamas uses its citizens to protect its forces.
“Those who fail to condemn, condone. Those who refuse to call Hamas terrorists allow the legitimising of their brutal deeds.”
Communities Secretary Michael Gove told the rally that “Britain stands with Israel”.
“There are no words to describe the suffering of families who have seen their relatives butchered in front of them and relatives who live in hope that those who were living peacefully in their homes just two weeks ago and are now in a Hamas dungeon should be freed,” Mr Gove said.
“No words can sum up the evil of those responsible for these acts.
“But words matter and promises matter and the world made a promise 75 years ago: Never again.
“And what did we see a fortnight ago? The biggest most horrific slaughter of Jewish people since the Holocaust, carried out by terrorists; an act of evil, unparalleled evil and barbarism.
"We must stand together against it. We must stand for life. We must bring the hostages home.
“There is a difference between now and 1945 and that difference is the Jewish people have a home, they have a nation. That nation was born in the hope to uphold humanity's greatest virtues," Mr Gove said.
“The [Israeli military] are there to protect civilians. Hamas exist to slaughter civilians.
“It breaks my heart to know that there are Jewish children who must disguise their school uniform to hide the fact that they got to a Jewish school.
“It breaks my heart that there are students at our universities who must hide the Star of David around their neck, or that there are Jewish individuals who dare not wear the wear the kippah on our streets for fear of what might be done.
“Our Jewish community must be protected.
"And when we see people on our streets with posters celebrating paragliding killers, when we see terrorist flags waved, when we see chants which call for the elimination of the Jewish state, then we must be clear: Never again shall we see these words, these symbols, this hate.”