About four years ago, one of the few passersby who dropped into Butterfield's enormous neo-Gothic barn of a church is St Augustine's on a prime piece of real estate in Queen's Gate, South Kensington, would have witnessed an extraordinary sight.

Hour after hour, standing at the altar, they would have seen an ex-offender with startling blue eyes, a shock of wavy brown hair and a face that has clearly 'lived' a little, practising the complex rituals and liturgy of a 34-page High Mass that owes more to 20th-century Rome than his own Church of England, until he knew every step by heart.

Rev Paul Cowley was awarded an MBE in the latest honours, for services to ex-offenders. His story and that of the church he now leads are living witnesses to the power of faith to transform.

Now 58, at 15 he was expelled from school and after living in a squat entered a life of crime which landed him behind bars. When he came out he found salvation in the Army after seeing a poster offering a 'life of adventure'. In 16 years he rose to Staff Sergeant, did three tours in Northern Ireland and one in the Falklands and fought on the Army boxing team. After leaving he became a fitness trainer and ended up running one of London's top fitness clubs. "The Army absolutely saved my life," he says. "It brought out leadership skills and self-discipline and gave me a family, clothes and fed me."

He was persuaded to do an Alpha course at HTB in 1994 and his life was turned around. "I came to Christ," he says. "God did a real number on me." The change came half way through the course. "I remember thinking, if all this stuff is true, I can change. I can be the person I want to be, a man of character, strength and integrity, a good husband, a good father. I remember thinking, God, if you can do all that, I am up for it. I finished the course, and things started to change." He became involved in running home groups, and then in ex-offender work after HTB staff heard his testimony and asked him to visit Dartmoor, which led to setting up Alpha for prisons. Eight in ten prisons now run the course.

He was ordained in 2002 after a three year degree course at Oakhill and in 2010 was appointed pastor of HTB Queen's Gate, under the oversight of HTB vicar Nicky Gumbel.

His work at St Augustine's, rechristened St Augustine's Queen's Gate, includes Alpha for Prisons, Caring for Ex-Offenders, Alpha for Forces, and the William Wilberforce Trust which takes in a counter-human trafficking unit, a homeless drop in, debt counselling and courses dealing with money, dept, depression, and recovery. There is a staff of 42 including 30 in the refurbished offices at the church itself.

St Augustine's is now the only church in the fast-expanding HTB stable where the main service is an Anglican High Mass, clouds of incense included.

When Paul arrived at the church, the roof was leaking, the lights were not working and there was a an elderly congregation of about 13. He decided to respect their tradition and, perhaps unusually for a church plant, instead of asking them to embrace the evangelical style, he embraced theirs.

HTB paid for a total refurbishment. The pews went, the enormous vicarage was turned into social housing, the fabric was restored. The ornate gilded reredos, the high altar and the High Church luminescent feel of the building remain.

With the help of friends at the nearby Brompton Oratory, one of the country's leading Catholic churches and now itself involved in HTB's ex-offender ministry scheme, the intricate gorgeously coloured silk and lace vestments were dusted off and sorted in their antique drawers in the vestry.

Paul balked only at wearing these, in particular refusing to wear the ornate gold cope, and prefers the traditional Anglican cassock, surplice and stole. He also declined to celebrate Mass with his back to the congregation. He faces them, from a new table installed at the top of the nave.

But the liturgy is unchanged, and the congregation has grown nearly ten-fold, enhanced by a professional robed choir with members drawn from the Royal College of Music.The early morning family service has moved there from St Paul's Onslow Square and there is now a Sunday afternoon worship service, with hundreds of people, in the evangelical style for which HTB is known. During the week, there are regular drop-ins for homeless people and those in need of debt, drug and other advice.

"Through the grace of God it has been extraordinary," says Paul. And he's only just begun.