The harmonium in the village church of Clarecastle, Co Clare, in the west of Ireland, was the only keyboard in the area available to me as a teenager. We didn’t have a piano at home. That was my first encounter with an instrument and so meant everything to me; it was a complete world. The poor thing didn’t know what hit it. I would pump it wildly to extract every ounce of volume possible – often to the distress of an old canon who sat in the church alone reading his breviary and meditating. There was just me, the harmonium and him. I played for masses, weddings, funerals, and became an expert on classical harmonium hits from opera, oratorio, symphony, sonata, parlour songs, hymns, carols and whatever else was going. I was completely at one with the fabric of the instrument, the various stops, the wood, the pedals, the wind, the smell, the usually freezing church, the light.

I also played occasionally at Ennis Cathedral, the main town in Co Clare, two miles away. The church sacristan hated me playing there for some reason and would sometimes switch off the power from the sacristy while I was playing. The organ would implode from lack of air.

I studied in Amsterdam with Piet Kee. He once gave me a lesson on the Haarlem organ – a magnificently scary experience. It was like trying to control a powerful horse – you were riding it as it was bucking under you. The lesson at Haarlem was on Bach’s Great B minor, the Prelude and Fugue BWV 544.

My career as church organist has been chequered. While a student in Dublin I was deputy organist at the Christian Science Church in Baggot Street. I earned 15 shillings per service. I played for some of their Sunday services and also for their Wednesday evening meetings in an upstairs room of a house nearby where members would declaim visions they’d had during the week and I’d accompany the hymns on an upright piano. But they said my playing was neither dignified nor grave enough. Their church was demolished some time later.

In Cologne, I had a good job at a Protestant church for a year, but when they found out that I’d lied about being Protestant and was in fact Catholic they fired me. It was a great pity because I got on well there and enjoyed playing for them, especially as the church was just down the street and I could stay in bed until the last bells before the services.

I then got a job outside Cologne at a Catholic church. I stayed there for quite a long time and had a flat attached to the church. Modest salary. I wrote my ensemble piece “______” on that organ. I never had a piano in those days. Because many of the masses were at 7am and because I’m hopeless at getting up early, I was sometimes late, and the sacristan hated me and would pound on my door to get me up. I would then arrive in the church to be greeted by the disapproving stares of 50 old ladies shortly after 7am.

I’ve never had luck with sacristans. The local power they have goes to their heads and they love wielding it. The parish priest was on my side, though, and protected me from the sacristan’s desire to be rid of me. I played for a lot of funerals in that church, rarely for weddings. Because there was tension between me and the congregation I would sometimes punish them by not waiting for them to breathe between phrases and would triumphantly arrive at the end of hymns before they did. Strangely, I wasn’t asked to leave that job – I decided to leave because I thought if I stayed much longer I’d go mad.

In my new organ concerto there is a solo for harmonium in remembrance of my beginnings on the instrument. Also the Angelus appears. That was a haunting marking of times of the day in my childhood. The bells at noon and in the evening – but especially the ones at noon. When you heard the bells you were supposed to stop whatever you were doing, be still and pray. I remember the silence over the whole village. I enjoyed feeling pious in those moments and admired myself for being it. Then when the bells ended you continued whatever you had been doing before, though in my case it was usually nothing.

There are 21 metronomes in the orchestra. The organist has one and the orchestra 20. I am very fond of the metronome, and its pyramid shape made me fond of Egypt.

There are always unexpected triggers in writing. For instance, I know a cat who lives in Washington Square in New York. His name is Blue Gadoo and he’s a very peculiar cat. I saw a photograph of him with a book called Sex and the Sacred in Wagner’s Tristan und Isolde. By his expression I knew he was mourning the loss of atonality. So I put his fight for atonality against tonality into the concerto.

I use musical phrases in the concerto that are like surreal familiar objects – as if I am seeing the ones from my harmonium village greatest hits compendium in another life – like when I die and go to heaven and hear them there. I’m sure they sound different there. Familiarly strange.

The concerto ends with the organ and orchestra joining in the hymn, Humiliated and Insulted.

• The world premiere of Gerald Barry’s organ concerto with Thomas Adès conducting the CBSO is at Symphony Hall, Birmingham, on 7 March. Adès conducts the London Philharmonic Orchestra in the London premiere on 11 April, broadcast live on Radio 3.