A Roman Catholic priest in Bradford, who sexually assaulted a teenage girl and had a secret wife, committed “gross breaches of trust”, his diocese has said.

William Finnegan, 59, was found guilty by a jury of assaulting the girl, who cannot be named, by kissing her forcefully on the mouth and touching her bottom.

He was told by the judge he could face immediate prison when he is sentenced in April.

Finnegan, known as ‘Father Bill’, was parish priest of St Clare’s in Fagley, at the time.

As part of his defence, he had revealed in court – and at the same time to his Diocese – that he had secretly married in Cyprus in 1999, despite having taken a vow of celibacy when he was ordained.

After the court hearing, a spokesman for the Roman Catholic Diocese of Leeds, which covers Bradford, expressed its “deep sense of shame” over Finnegan’s actions and confirmed he would be unable to return to the priesthood.

A statement by Monsignor John Wilson, Diocesan administrator, said: “I first want to express my deep sense of shame at the actions of William Finnegan. I also want to express my sorrow and regret to his victim. I realise that this has been a very difficult and distressing time for you and your family. My thoughts and prayers are with you and my door is open to you.”

During the trial, at Bradford Crown Court, prosecutor Richard Walters said Finnegan had told the girl he loved her, before sexually assaulting her on Easter Sunday last year.

He said: “The defendant grabbed [the girl], pulled her towards him, placed a hand on her bottom and proceeded to kiss her forcefully and passionately with an open mouth.

“Two days later he visited her home address and told her he had sexual feelings towards her.”

During the trial it had been revealed that Finnegan had been in a secret marriage for more than a decade with a former parishioner, Beverley Dawson, despite having taken a vow of celibacy.

The revelation was made as his barrister, Jeremy Hill-Baker, opened the case for the defence, who said the jury would be hearing evidence from both Finnegan and his wife.

He said: “No, you didn’t mishear me. His wife. He and Beverley Dawson secretly married abroad in September 1999. So deeply in love was he that he was prepared to ignore the Catholic Church’s ban on marriage, a secret which has been kept from almost everyone until now.”

At about 12.30pm yesterday, the jury of nine women and three men found Finnegan guilty of sexual assault, by a majority of 11 to one, after deliberating for five hours and 30 minutes.

Finnegan gave no reaction as the verdict was read to the court, but there were gasps from the packed public gallery. Mrs Dawson, Finnegan’s wife, was not present.

Finnegan’s sentencing has been adjourned until April 11, but the Recorder of Bradford, Judge Roger Thomas QC, warned him one sentencing option was “immediate imprisonment”.

He will also have to sign the sex offenders’ register.

Finnegan, of Acacia Close, Castleford, was released on conditional bail.

He was told not to contact his victim or any of the witnesses in the case, and he must not visit St Clare’s RC Church in Fagley.

•The full statement by Monsignor John Wilson, administrator of the Roman Catholic Diocese of Leeds, said:

On March 15, 2013, William Finnegan, who served as a Catholic priest in the Diocese of Leeds, was convicted following a five-day trial at Bradford Crown Court of the sexual assault of a 17-year-old girl.
I first want to express my deep sense of shame at the actions of William Finnegan.
I also want to express my sorrow and regret to his victim. I realise that this has been a very difficult and distressing time for you and your family. My thoughts and prayers are with you and my door is open to you.
It emerged during the trial that William Finnegan, contrary to the discipline of the Catholic Church had married in a civil ceremony in Cyprus in 1999.
This news was as shocking to the officials of the Diocese as it was to all those present in court and is another example of the gross breaches of trust committed by William Finnegan.
I will be making a special visit this weekend to St Clare’s Parish, Bradford, where William Finnegan served as parish priest, as an expression of the Diocese’s commitment to support and care for all those touched by his actions.
The Diocese is committed to ensuring the safety and protection of every child and vulnerable person in our parishes and there are robust safeguarding policies and procedures in operation throughout the Diocese – and indeed the Catholic Church in England and Wales.
As with this case, any abuse reported to the Diocese is referred to the police and other relevant authorities and the Diocese of Leeds cooperated fully with the police throughout this case.
I wish to make clear that William Finnegan voluntarily stepped down from his role as parish priest for the duration of the criminal proceedings and Bishop Roche withdrew his priestley Faculties.
In light of this conviction and his entering into civil marriage he will be unable to return to priestly ministry.
If anyone has any concerns at all relating to this matter, please contact the Diocesan Safeguarding Co-ordinator.”