One of the country's leading Roman Catholic bishops resigned 'in shame' today after admitting to a relationship that broke his clerical vows.

In a scandal that will rock the Church, the Bishop of Arundel and Brighton, Kieran Conry, said he had been 'unfaithful to his promises'.

Separately, a Mail on Sunday investigation has revealed the bishop also had a love affair with a married mother of two.

Scroll down for video

Bishop Kieran Conroy insisted he was resigning over a previous relationship, rather than the one he had with the married mother-of-two (pictured)

This newspaper has seen love letters between Bishop Conry, 63, and the woman, written in recent months, in which he tells her that her husband doesn't love her.

One handwritten letter, which was dated earlier this month and addressed 'Dear, Dear XXXXX' and signed 'your K xxxxxx', said: '… It's all right to say that [your husband] did bad things, but you knew that he didn't love you. You know (I hope) that I did. And I did, and do.'

The passionate correspondence, using language reminiscent of the movie Brief Encounter, reveals the pair fell deeply in love and formed a strong emotional bond.

Although the letters do not disclose a sexual relationship, the affair lasted more than a year and involved the married woman spending at least three nights at the bishop's detached property in Pease Pottage, West Sussex.

The Mail on Sunday has also seen a love letter from the bishop to a second woman, whose name we are not publishing for legal reasons.

The bishop insisted that the affair with the mother of two was not the reason for his resignation. He said he had quit over a different relationship.

Confronted at his home last night, he said: 'This has nothing to do with your enquiries. It is totally unrelated. This relates to a relationship of six years ago. So be careful what you write. This had nothing to do with your earlier questions.'

Approached by this newspaper in June, the bishop denied any sexual relationship with the married woman but admitted she had stayed at his house twice, adding: 'She is not the only woman who has stayed here.'

Bishop of Arundel admitted that the married 43-year-old had stayed over at his house for at least two nights

The 43-year-old woman was also spotted shopping with him on a Saturday afternoon in Brighton in June and the pair exchanged hundreds of text messages, according to the woman's husband.

Bishop Conry admitted he had been seen in public with the mother of two. He said they had been to the British Museum, a Matisse exhibition and the ballet together.

The woman's estranged husband, who employed a private detective to track her movements, accused the bishop of 'appalling behaviour', and he is preparing to launch a legal action against the Church.

Bishop Conry, seen as a progressive who has been critical of the Vatican's hard-line pronouncements, is close to the head of the Church in England and Wales, Cardinal Vincent Nichols.

Last night, the bishop, who is sworn to celibacy, said in a statement to be read in churches: 'I am sorry to confess that, going back some years, I have been unfaithful to my promises as a Catholic priest.

'I would like to reassure you that my actions were not illegal and did not involve minors. As a result, however, I have decided to offer my resignation as bishop with immediate effect and will now take some time to consider my future.

'I want to apologise to the individuals hurt by my actions and then to all of those inside and outside the diocese. I am sorry for the shame that I have brought on the diocese and the Church and I ask for your prayers and forgiveness.'

Cardinal Nichols said: 'This is a sad and painful moment. All involved in this situation are much in my prayers today.'

Bishop Conry and the married woman, whom we are not naming for legal reasons, are understood to have become close after she and her husband joined the bishop in church activities last summer. It is believed their relationship began to flourish only after her marriage hit a crisis last year.

Parishioners say she moved out of the marital home at the turn of the year and has subsequently moved into a rented house in West Sussex. Since then she has been a regular visitor to the bishop's residence. Her husband told The Mail on Sunday: 'His behaviour has been appalling. He is someone capable of creating that emotion and distress without taking any interest in the effect on those going through this.

'It smacks of arrogance, and arrogance to the extent that he is prepared to have a married woman sleeping in his house, a woman with two children, and yet he is blind to the emotional effect of this. For me it has been debilitating to the extent that I have felt ill.

'There has been the gradual realisation that I am going to have to deal with this in a mature and sensible way and this has helped me. You have to fight for your children and make sure their future is not in the hands of someone like this.'

The man filed for divorce earlier this month. He added: 'The bishop is supposed to set the best example for a lot of people. To think that this is a person who people turn to for marriage advice is unbelievable. It makes him a hypocrite.'