It was no secret that Mohandas Gandhi had an unusual sex life. He spoke constantly of sex and gave detailed, often provocative, instructions to his followers as to how to they might best observe chastity. And his views were not always popular; "abnormal and unnatural" was how the first Prime Minister of independent India, Jawaharlal Nehru, described Gandhi's advice to newlyweds to stay celibate for the sake of their souls.

But was there something more complex than a pious plea for chastity at play in Gandhi's beliefs, preachings and even his unusual personal practices (which included, alongside his famed chastity, sleeping naked next to nubile, naked women to test his restraint)? In the course of researching my new book on Gandhi, going through a hundred volumes of his complete works and many tomes of eye-witness material, details became apparent which add up to a more bizarre sexual history.

Much of this material was known during his lifetime, but was distorted or suppressed after his death during the process of elevating Gandhi into the "Father of the Nation" Was the Mahatma, in fact, as the pre-independence prime minister of the Indian state of Travancore called him, "a most dangerous, semi-repressed sex maniac"?

Gandhi was born in the Indian state of Gujarat and married at 13 in 1883; his wife Kasturba was 14, not early by the standards of Gujarat at that time. The young couple had a normal sex life, sharing a bed in a separate room in his family home, and Kasturba was soon pregnant.

Two years later, as his father lay dying, Gandhi left his bedside to have sex with Kasturba. Meanwhile, his father drew his last breath. The young man compounded his grief with guilt that he had not been present, and represented his subsequent revulsion towards "lustful love" as being related to his father's death.

However, Gandhi and Kasturba's last child wasn't born until fifteen years later, in 1900.

In fact, Gandhi did not develop his censorious attitude to sex (and certainly not to marital sex) until he was in his 30s, while a volunteer in the ambulance corps, assisting the British Empire in its wars in Southern Africa. On long marches in sparsely populated land in the Boer War and the Zulu uprisings, Gandhi considered how he could best "give service" to humanity and decided it must be by embracing poverty and chastity.

At the age of 38, in 1906, he took a vow of brahmacharya, which meant living a spiritual life but is normally referred to as chastity, without which such a life is deemed impossible by Hindus.

Gandhi found it easy to embrace poverty. It was chastity that eluded him. So he worked out a series of complex rules which meant he could say he was chaste while still engaging in the most explicit sexual conversation, letters and behaviour.

With the zeal of the convert, within a year of his vow, he told readers of his newspaper Indian Opinion: "It is the duty of every thoughtful Indian not to marry. In case he is helpless in regard to marriage, he should abstain from sexual intercourse with his wife."

Meanwhile, Gandhi was challenging that abstinence in his own way. He set up ashrams in which he began his first "experiments" with sex; boys and girls were to bathe and sleep together, chastely, but were punished for any sexual talk. Men and women were segregated, and Gandhi's advice was that husbands should not be alone with their wives, and, when they felt passion, should take a cold bath.

The rules did not, however, apply to him. Sushila Nayar, the attractive sister of Gandhi's secretary, also his personal physician, attended Gandhi from girlhood. She used to sleep and bathe with Gandhi. When challenged, he explained how he ensured decency was not offended. "While she is bathing I keep my eyes tightly shut," he said, "I do not know ... whether she bathes naked or with her underwear on. I can tell from the sound that she uses soap." The provision of such personal services to Gandhi was a much sought-after sign of his favour and aroused jealousy among the ashram inmates.