Mother Teresa of Calcutta, who has been put on the “fast track” to sainthood, was so tormented by doubts about her faith that she felt “a hypocrite”, it has emerged from a book of her letters to friends and confessors.

Shortly after beginning her work in the slums of Calcutta, she wrote “Where is my faith? Even deep down there is nothing but emptiness and darkness. If there be a God — please forgive me.”

In letters eight years later she was still expressing “such deep longing for God”, adding that she felt “repulsed, empty, no faith, no love, no zeal”.

Her smile to the world from her familiar weather-beaten face was a “mask” or a “cloak”, she said. “What do I labour for? If there be no God, there can be no soul. If there be no soul then, Jesus, You also are not true.”

Mother Teresa, who died in 1997 and was beatified in record time only six years later, felt abandoned by God from the very start of the work that made her a global figure, in her sandals and blue and white sari. The doubts persisted until her death.

The nun’s crisis of faith was revealed four years ago by the Rev Brian Kolodiejchuk, the postutalor or advocate of her cause for sainthood, at the time of her beatification in October 2003. Now he has compiled a new edition of her letters, entitled Mother Teresa: Come be My Light, which reveals the full extent of her long “dark night of the soul”.

“I am told God lives in me — and yet the reality of darkness and coldness and emptiness is so great that nothing touches my soul,” she wrote at one point. “I want God with all the power of my soul — and yet between us there is terrible separation.” On another occasion she wrote: “I feel just that terrible pain of loss, of God not wanting me, of God not being God, of God not really existing.”

Rev Kolodiejchuk maintains that Mother Teresa did not suffer “a real doubt of faith”, but that, on the contrary, her agonising demonstrates her faith in God’s reality. “We cannot long for something that is not intimately close to us . . . Now we have this new understanding, this new window into her interior life, and for me this seems to be the most heroic,” he said.

The priest said that the Church authorities had decided to keep her letters even though one of her dying wishes was that they should be destroyed. In one, written to a spiritual adviser, Michael van der Peet, shortly before she received the Nobel Peace Prize in 1979, she wrote that: “Jesus has a very special love for you. As for me, the silence and emptiness is so great that I look and do not see, listen and do not hear. The tongue moves but does not speak.”

The late Pope, John Paul II, a great admirer of Mother Teresa, began the process of beatification immediately after her death. This required proof of a miracle cure performed through her intercession, and in 2002 the Vatican recognised as a miracle the healing of a stomach tumour in an Indian woman, Monica Besra, who laid a locket containing Mother Teresa’s picture on her abdomen. A second miracle is required for the nun to proceed to canonisation.