The head of Britain’s diplomatic service has said Lord Balfour “wanted his words to have historic effect” but that his Declaration would have included the right of Palestinian self-determination if written a few decades later.

Sir Simon McDonald, Permanent Under-Secretary at the Foreign and Commonwealth Office, made the comments during a keynote speech at Portcullis House, Westminster.

Speaking at the beginning of the Jewish News-BICOM policy conference considering Britain, Israel and the Middle East 100 years after the Balfour Declaration, McDonald said the 67-word letter “set the tone for UK-Israel relations,” built up over decades.

As Israeli Prime Minister Benjamin Netanyahu visited British Prime Minister Theresa May in London, McDonald described the UK as “a close friend of Israel and has an unshakeable commitment to Israel’s right to exist, and its security”.

McDonald, who has served in Berlin, Jeddah, Riyadh, Bonn, Washington and Tel Aviv, entering the diplomatic service more than 35 years ago, acknowledged that the Middle East is a region “not without controversy in analysing trends”.

He said: “When trying to make sense of the present, we cannot ignore the controversies of the past, and we cannot ignore the negative feeling from Palestinians and the Arab world about the Balfour Declaration that still persist today.”

He added: “Despite these difficulties, it is clear that the BD was a pivotal moment in the long process that preceded the founding of the State of Israel and the British government remains proud of the role the British government played in helping to make the Jewish homeland a reality.”

As a historian, McDonald said he was interested in the historical, political, military, diplomatic and moral forces motivating Balfour and the War Cabinet in 1917, asking how critical the Balfour Declaration was in the creation of the State of Israel.

McDonald said his predecessor in 1917, a 23-year old peer, opposed the Declaration with good reason. Lord Harding, permanent under-secretary 100 years ago, was not unsympathetic to the Zionist cause, but opposed the declaration because he “distrusted general pledges” and had “concerns about giving encouragement to a movement based on conditions we cannot enforce”.

McDonald said of Harding: “He was right, because in the end the Balfour Declaration was important, but it was the hope, energy, determination and ingenuity of Jewish immigrants to Mandate Palestine, as well as the hundreds of thousands of Holocaust survivors, that led to the creation of Israel, 31 years after Balfour’s declaration.”

Britain’s most senior diplomat conceded, however, that Balfour’s letter “was a key moment along the way, and the British government is proud that we played our part, but it was the people on the ground that played the most decisive role”.

He said: “As we work on advancing the UK-Israel relationship, it is important that we also work to fulfil all parts of the Declaration,” adding: “The second part of Balfour’s Declaration remains unfinished business.”

The second element, known as a saving clause, expressed that “nothing shall be done to prejudice the civil and religious rights of the existing non-Jewish communities in Palestine”.

McDonald said: “If written after the Second World War, when the international community developed a rules-based international architecture, the Declaration would have included the political rights of self-determination of these communities too.”

He added: “We want to see a lasting peace that fulfils the whole of the Balfour Declaration.”