In 1974, the New York Times journalist Bernard Weinraub described India as "the loneliest post in the world" for Israeli diplomats. Having voted against the creation of Israel at the UN in 1947, India held back from establishing full diplomatic relations with Tel Aviv until 1992. For decades, Israel's presence in India was limited to an immigration office in Mumbai. In between, India voted with the majority to pass UN resolution 3379, condemning Zionism as a form of racism, became one of the first non-Arab states to recognise Palestine's declaration of independence in 1988, and was generally among the more vocal non-Arab voices against Israel.

Today, India is Israel's closest eastern ally and its largest arms market. Annual non-military bilateral trade alone exceeds $4.5bn. Since 2001, the diasporas of the two countries have emerged as energetic allies against a shared enemy: Islamic extremism. A survey by the Israeli foreign ministry in 2009 found India to be the most pro-Israel country in the world, well above the US. Once a bastion of pro-Palestinian sentiment, India recently appeared at the bottom in a worldwide poll of countries sympathetic to Palestinian statehood. Throw a stone in Panaji and it is likely to land on an Israeli backpacking through India after his post-mandatory service.

What precipitated this dramatic shift? Israel had all along been a quiet ally of New Delhi, volunteering clandestine support as India sought to repel attacks by China (in 1962) and Pakistan (in 1965). Israeli officials knew also that India, which had no history of anti-semitism, had arrived at its Israel policy through a combination of post-colonial hauteur, realpolitik – particularly its desire to placate Arab opinion in its contest against Islamic Pakistan – and an ethical commitment to the Palestinian cause. Partly for these reasons, India's anti-Israel actions rarely provoked any anxiety in Tel Aviv.

There are three principal reasons behind the shift in India's attitude. The first is the belated realisation that no amount of deference to Arab sentiment could alter Muslim opinion in the Middle East in India's favour: when it came to Kashmir, Shia and Sunni united in supporting Pakistan's position. The second owes itself to the collapse of the old world order: the death of the Soviet Union meant that India had to seek out new allies. The third factor that contributed to the deepening of Indo-Israeli ties is less well-known: the rise of Hindu nationalism in India.

To votaries of Hindu nationalism, Israel is something of a lodestar: a nation to be revered for its ability to defeat, and survive among, hostile Muslims. As the liberal Israeli newspaper Haaretz put it, "Relations between Israel and India tend to grow stronger when … India experiences a rightward shift in anti-Muslim public opinion or in leadership".

This explains why Hindu opinion is inflamed even by the most anodyne Indian expression of solidarity with Palestine. At the UN general assembly last month India's prime minister, Manmohan Singh, offered some somniferous words of support for Palestine's membership effort: "India is steadfast in its support for the Palestinian people's struggle for a sovereign, independent, viable and united state of Palestine with East Jerusalem as its capital, living within secure and recognisable borders side by side and at peace with Israel".

No one in Israel seemed to have noticed. None of the major newspapers editorialised it. There wasn't even a specific news item in the Israeli press singling out India. Trade did not suffer. The markets registered no shifts. But this did not deter some Indians from rising to take offence on Israel's behalf. To Sadanand Dhume, a US based commentator who published a hysterical philippic in the Wall Street Journal castigating India for not "throwing its weight behind Israel", Singh's speech was nothing short of a "foreign policy mishap". According to Dhume, who has since been ordained "the go-to guy for all matters India" by an excited colleague of his: "Both India and Israel represent ancient civilisations whose land carries a special spiritual significance for most of its people."

This desire to define citizenship and belonging in the procrustean terms of ancient culture over all other considerations is where Hindutva and Zionism converge. As Koenrad Elst, one of the most influential producers of pro-Hindutva pabulum, has said of the movement's founder, "Veer Savarkar was the Hindu counterpart of a Zionist: he defined the Hindus as a nation attached to a motherland, rather than as a religious community". "True, there is an obvious difference between the situation of the Jews, who had to migrate to their motherland … and the Hindus who merely had to remove the non-Hindu … regime from their territory." This prescription for ethnic cleansing came to life in 1992, when Hindu nationalists brought down the Babri mosque in the northern Indian city of Ayodhya. Their ongoing struggle to seize the Babri land, which belonged to Muslims for over five centuries, looks to Israel's appropriation of Palestinian territory as a useful template.

In 2009, Mumbai's anti-terror squad arrested, among others, an officer in the Indian army, Prasad Purohit, for masterminding a terrorist attack on Pakistani citizens and plotting to overthrow the secular Indian state. In his confession, Purohit admitted to making plans to approach Israel for help. It says something about the state of Israel when the most virulently anti-Muslim terrorists in India reflexively look to it as a potential source of support.

This is tragic – because, in the minds of the formidable men who willed them into existence, India and Israel were alike. Theodor Herzl's conception of Israel was remarkably similar to Mahatma Gandhi's idea of India. Both men refined their ideas gradually. In Der Judenstaat, Herzl presented Israel as a "rampart of Europe against Asia, an outpost of civilisation as opposed to barbarism". Several years later, he offered a more coherent version, a blueprint for a modern pluralistic state, operating under the aegis of Jews, but self-consciously inclusive: visionary Jews and welcoming Arabs people his extraordinary novel Altneuland, one of the founding texts of Zionism. Herzl resolved the conflicts of conscience by transmitting some of the most powerful arguments for Israel's establishment through an Arab character, Reshid Bey. "It was a great blessing," Reshid explains to a sceptical visitor. "Nothing could have been more wretched than an Arab village at the end of the 19th century … [The Arabs] are better off than at any time in the past." But Herzl was alert to the victim's capacity to victimise. In Dr Geyer, we are shown a chilling vision of majoritarian zealotry: a fanatical rabbi, he wants all Arabs expelled from the New Society. Redemption comes in the form of David Littwak, the son of a peasant who believes in a land for all, Arab and Jew, and whose opposition to and victory over Geyer is cast as the highest affirmation of Zionism. Unlike Herzl, Gandhi scorned modern technology for most of his life. In his early life, Gandhi's politics were conspicuously exclusionary. But the India he imagined even after alighting on his Satyagraha campaign relied on a network of Indian David Littwaks to survive. It was a dream that crashed during his own lifetime, with the partition of India.

Today, some of the most powerful politicians in Israel are those who violate Herzl's ideas. Avigdor Lieberman, a Russian immigrant foreign minister of Israel, has openly echoed Geyer's thoughts, calling for the expulsion of Israeli Arabs. In Gandhi's home state, Narendra Modi, a rabidly anti-Muslim politician implicated in the anti-Muslim pogrom of 2002, continues to secure handsome mandates from the largely Hindu electorate.

India's support for Palestine is one of the last remaining precepts from time of Pandit Nehru, India's first prime minister who is loathed by Hindu chauvinists for refusing to turn India into a "Hindu Pakistan". As per the Hindu nationalist narrative, the Congress party's support for Palestine – if such a thing actually exists in any meaningful sense – is a bribe to Indian Muslims. In reality, Indian Muslims have made noticeable efforts to build bridges with Israel. But if anyone can be accused of holding foreign policy hostage to religious bigotry, it is the Hindu nationalist BJP. During its disastrous term in power, from 1997 to 2004, ministers in the government dismissed pro-Palestinians as "more Palestinian than Palestinians themselves". Its foreign minister, Jaswant Singh, suggested that a common civilisational outlook bound India and Israel – implying that Indian Muslims who shared the faith of the Arab majority were somehow alien to India's "civilisation".

India and Israel have much to offer each other and Israel's security must figure as a non-negotiable precondition in New Delhi's support for Palestine. But Hindu nationalists are not concerned with the security of Israel: it is the abandonment of Palestinians they seek.

The seeds of Israel's redemption are embedded in Zionism, which is concerned with housing people, not displacing them. Israel must merely embrace it. It will still be a paternalistic form of "pluralism", but it will be inclusive. On the other hand, Hindutva's very purpose is the disenfranchisement and abolition of religious minorities. So Israelis must wonder what has become of them, their nation, that their most fervid admirers in the most pro-Israeli country in the world happen to be fascists. Until Israel and India undertake an honest reappraisal of their friendship, those who care about the ideas of Herzl and Gandhi must acknowledge this much: theirs is an alliance deepened by prejudice.