In April 1962, Sir Winston Churchill joined Aristotle Onassis on board his yacht, Christina, for a Mediterranean cruise. Setting sailing from Monte Carlo, the Greek shipping billionaire and the former Prime Minister headed for Libya, Lebanon and Greece.

Alarm bells, however, were soon ringing at the highest levels of the British state. “I fear much,” Churchill’s panicked private secretary wrote to Downing Street civil servants, “that Sir Winston will insist on visiting Israel. I will do what I can to persuade Sir Winston not [to], but I cannot guarantee it in view of his long association with Israel and his outspoken feelings as a Zionist.”

It might be necessary, the note concluded, for Harold Macmillan to write to his one-time boss and appeal to him not to drop anchor in Israeli seas and head ashore.

In the end, this potential diplomatic disaster was averted: Christina slipped along the Israeli coast in the dead of night. Churchill would never visit the state whose creation he had for so long fervently supported.

That, nearly two decades after its establishment, consideration was given to trying to prevent Churchill — even at 87, as strong-willed as he was dogged in his Zionism — from visiting the Jewish state offers a small illustration as to why no member of the royal family has ever officially done so.

It will be especially fitting if this, the centenary year of the issuing of the Balfour Declaration, is the moment at which this apparent boycott comes to an end. For it is Balfour that shaped much of the Foreign Office’s nervousness about Israel; a nervousness which bears much of the responsibility for the fact that a royal visit has never been sanctioned.

In the eyes of the men of King Charles Street, Balfour represented Britain’s Middle Eastern original sin: the baleful consequences of which — the re-establishment of a Jewish homeland in the land of Israel — left it uniquely exposed to the anger, hostility and revenge of the Arab states. Atoning for Balfour to protect Britain’s commercial, defence and strategic interests in the region thus became the principal driver of policy.

It would take nearly 40 years for a serving British prime minister to set foot in Israel. Margaret Thatcher’s 1986 visit thus represented a significant staging post in what Neill Lochery has described as the long and bumpy road towards normalising relations between Britain and Israel.

Thirty years on, a royal visit would mark the giving of an official seal of approval that has been quite consciously withheld.

Whenever members of the royal family have visited Israel — Prince Charles attended both the funeral of Yitzhak Rabin in 1995 and Shimon Peres last autumn, while in 1994 the Duke of Edinburgh went to the Mount of Olives where his mother, Princess Alice of Battenberg, is buried — Buckingham Palace has been quick to make clear that these were not official visits.

It is not through a lack of asking on Israel’s part. In 1997, the Israeli president, Ezer Weizman, paid an official state visit to Britain. Despite the fact such visits are almost always reciprocated, and Weizman personally invited the Queen to Israel, no such return visit was forthcoming. Two years ago, Benjamin Netanyahu used a brief meeting with Prince Charles at the Paris climate-change conference to invite the heir to the throne to pay an official visit.

A hint as to the fears which surround such a visit — and to the heavy dose of double-standards which surround the entire issue — was provided by the emails between Sir Michael Peat, who was then Prince Charles’s principal private secretary, and Clive Alderton, his deputy, which were leaked to the JC 10 years ago.

Referring to an invitation from the then Israeli ambassador to the prince, Alderton wrote: “Acceptance would make it hard to avoid the many ways in which Israel would want HRH to help burnish its international image.”

Curiously, concerns as to how Charles’s visits to Saudi Arabia and the Gulf states — or his mother’s to China or any of the dictatorships which the royal family have frequently been called upon to visit by the Foreign Office to flog British arms and other exports — might be exploited by unsavoury regimes with appalling human rights records to “burnish their international image” appear to have been overcome.

This anomaly has not escaped notice in Israel. As the late David Landau, the former editor of Haaretz, noted five years ago: “Is there another member-state of the United Nations that the British Royals have so consistently and assiduously snubbed in this way?”

But it is maybe less fear of how Israel might exploit an official visit for its own purposes and more worries about the royals’ own image which also helps explain this apparent snub.

One former senior Foreign Office official has privately suggested that the Queen has stayed away from Israel because her whole brand has been built upon the avoidance of controversy.

While visits by prime ministers to the country have largely passed off without incident, the Foreign Office is acutely aware that other senior politicians have not escaped so unscathed. In 1998, the then foreign secretary, Robin Cook, insisted on visiting the controversial Jewish neighbourhood of Har Homa in East Jerusalem.

Mobbed by Israeli demonstrators and accused of breaking agreed arrangements for the visit, the Israeli government cancelled his dinner with Netanyahu.

Three years later, Cook’s successor, Jack Straw, found meetings with both Prime Minister Ariel Sharon and President Moshe Katzav pulled when, on a post-9/11 Middle East tour, he appeared to suggest that terrorism in the region was fuelled by Israel’s policies in the West Bank and Gaza.

At the same time, Boris Johnson’s forthrightly expressed views on the BDS movement when he visited Israel as London mayor 18 months ago, led a number of Palestinian groups to refuse to meet him.

It is, however, precisely because the royal family are non-political that they can better avoid such controversies while still sending a powerful signal. Without a royal word being uttered, images of, for instance, Prince Harry, visiting a Tel Aviv tech company, kicking around a football with Israeli and Palestinian children at a coexistence project and laying a wreath at a Commonwealth war graves cemetery would underline the UK’s dim view of the BDS movement, its desire for peace and reconciliation between Arabs and Jews, and the historic ties which bind Israel and Britain.

The thaw in relations between Israel and the Sunni Arab states and the need to drum up new trade for a post-Brexit Britain further changes the calculus of risk that has hitherto kept the royals from the Holy Land.

After decades of avoiding a royal visit, perhaps Britain has also simply run out of excuses.

When Mrs Thatcher was questioned during her visit 30 years ago as to when the Queen would come, she replied: “But I’m here.”

Like so many of the former Prime Minister’s best lines, it’s not one which is likely to trip quite so easily or convincingly from Theresa May’s lips.