Gordon Brown has called the late Sir Martin Gilbert an “unforgettable friend” who helped him “again and again with his wisdom.”

At a memorial on Tuesday night in front of close to 600 guests including Holocaust survivors, members of the Churchill family and ambassadors, the former Prime Minister revealed that Sir Martin was to be made a Lord before his health declined in 2012.

Mr Brown also told the audience at Western Marble Arch Synagogue in central London that the next book written by Sir Martin – who was Winston Churchill’s official biographer - was to be about Labour’s most recent spell in Downing Street.

“Martin had agreed to make his next book a chronicle of our period in government,” he said, and prompting laughter from the crowd, added: “and what he would've made of us all, I guess we’ll never know.”

Mr Brown also revealed that the historian and scholar, who penned epic tomes on Jewish history, Israel and the World Wars before his death in February, had helped him to make the first speech given by a British Prime Minister to the Knesset - and then had inadvertently further helped diplomatic ties.

“When the [former] Prime Minister Ehud Olmert and I exchanged presents, it’s a reflection of Martin’s pre-eminence and our shared admiration of him that without either of us knowing it, I had chosen to give Olmert a copy of Martin’s The Righteous, and Olmert had chosen to give me a copy of Martin’s The Story of Israel.”

Mr Brown concluded his speech by paying heartfelt tribute to a man who he said “sailed the river of life brilliantly”.

“Our hearts will still ache at his loss but he leaves behind imperishable works that will never be lost, and he lives on in the impact he has on all of us, on the millions who he never met but who meet him in the pages that he wrote.”

He continued: “And every one of this great, large group of friends who come today to honour Martin from all over the world will not only never forget him, but as long as we live we will never cease to be inspired by the light and the learning he gave to us, to our country, and to the world.”

Rabbi Lord Sacks also commended Sir Martin in a moving speech, saying: “He was such a very special person. We loved him, we admired him - we miss him.”

The former Chief Rabbi recalled an event before the Holocaust Exhibition opened at the Imperial War Museum in June 2000, when survivors came to a dinner organised for them to see the display before it opened.

“I dreaded that moment,” he confessed. “But I needn't have worried. They were exuberant. It was as if they were at a wedding. They proceeded to talk through my speech, through Martin’s speech.

“It was just like being in shul.”

He said it was at that moment that he realised how Sir Martin, “in telling the story of the Holocaust and many other stories, lifted the burden from so many broken hearts.

“He was the person who gave voice to the voiceless.”

Speaking in soft, emotive tones, Lord Sacks told guests that Sir Martin had “showed more powerfully than anyone I ever met that history is an especially Jewish vocation”.

“He understood that to be a Jew is to make memory a religious duty. Martin had this phrase written on his heart - Moses tells the future generations: ‘Remember the days of old.’ That was the religious duty he had.

“We don’t make monuments for those who have died; their words are their memorial. Martin gave so many people their memorial.”

In a short speech, Lady Gilbert described her late husband as “a man of passion and compassion, who influenced the world as much as he wrote its history.”

Rabbi Nicky Liss, the minister at Highgate United Synagogue, said that though he only knew Sir Martin for a few years, “the wisdom he taught me gave me a completely new perspective on how to view the world. He taught me the importance, power and relevance of the individual in history.

“A blessing to the whole world, to the Jewish race and to Great Britain, Martin was also a jewel in the crown of our community.”