Rabbi Jeremy Gordon made the call on behalf of Noam Sagi whose 75-year-old mother was abducted by Hamas.
The British son of a retired Israeli teacher held hostage by Hamas has called for a humanitarian corridor to be established in Gaza.
Noam Sagi’s 75-year-old mother, Ada, was taken from her home in Kibbutz Nir Oz near the border with Gaza on October 7.
Mr Sagi, 53, did not speak at a vigil for the incursion’s victims in London’s Parliament Square on Sunday, but Rabbi Jeremy Gordon, of New London Synagogue, did speak on his behalf.
Hundreds gathered for the vigil and many of them were draped in Israeli flags.
They held signs saying “bring them home” on one side with pictures of the hostages on the other.
The grassroots-organised vigil featured speeches as well as prayer, singing in Hebrew and a testimonial from a woman named only as Lital, who was at the Nova music festival where hundreds were killed, read out by speaker Jenny Kananov Shayo.
More than 10 police officers were seen keeping watch over the vigil which lasted about an hour.
The rabbi said Mr Sagi’s mother “worked for peace between Jews and Arabs for decades” and taught Arabic as well as Hebrew.
The rabbi added: “Noam wants us to join with him in a demand that all the hostages be freed immediately and unconditionally, in particular, the children and those over 65.
“His second call is that a humanitarian corridor be opened to allow an appropriate organisation to verify who is there and to assess their most basic human needs.
“Ada is among the list of those missing who needs ongoing medical support.
“An organisation … should be allowed into Gaza safely to assess and provide for the most basic human needs of these hostages.
“It is an affront to everything that is human to take such people and to hide such people.
“He needs, we all need, the British Government to do anything that they can to get these people back.
“To show leadership internationally, to ensure the return of all civilian hostages, especially the women and the children, immediately.
“He wishes a representative of this Government would reach out to him directly. Noam deserves you to be directly in touch to show solidarity and to be inspired to fight for the release of these hostages.
“His message to the Israeli government is this. You have a responsibility to protect the civilians who lived along this border.
“To any representative of the Israeli government, Noam calls on you to do everything in your power to get these people out.
“Any pathway should be exploited, any government, any organisation can be contacted.
“Noam carries no hate for the people of Gaza. He carries no hate for people who are Muslim, no hate for the Arabs, no hate for the Palestinians. His love of all humanity remains resolute.”
Mr Sagi told a press conference in London on Thursday that the incursion amounts to a “second Holocaust”.
He told reporters there: “I should not be sitting here today. I should be on my way to Heathrow to pick up my mum … to celebrate her 75th birthday today.
“I am here because of pure evil.”