THE City Chamber Choir celebrated its 25th anniversary last year. It was founded by Stephen Jones with the intention of exploring unusual or neglected repertoire, with an emphasis on British composers. This it does by a combination of imaginative programme-building and very high standards of execution, as was demonstrated at its recent concert at the church of St Mary-at-Hill, in the City of London.

The contemporary composers James MacMillan and Gabriel Jackson were contrasted with their 16th-century counterparts Palestrina and William Byrd. Yet despite the contrasts the family resemblances were readily apparent, not only in the use of traditional words and forms - for example, MacMillan's Miserere and Jackson's Requiem - but also in the sound world they occupy, common vocal ground that enabled this talented choir to move from one style to another without undue disturbance.

That is not to say that it all sounded the same - far from it -but voices can often become technically disorientated and take some time to settle down to a contrasted style after something very different.

The City Chamber Choir - 25-30 voices - takes this in its stride, and the conductor Stephen Jones is clearly responsible; for he, too, is a singer. In a published interview last year, he recalled his own early experiences "of watching people training choirs who didn't seem to know much about singing". It stands to reason that if an orchestral conductor is expected to have a working knowledge of a wide range of instruments and considerable skill as an executant in one or two (or more) of them, a choral conductor should display similar technical ability.

The second half of the programme was devoted to Jackson's Requiem - first performed in 2008 - and it is hard to imagine how a choir of non-professional singers would interpret and execute the many complex technical requirements without very specific instruction from an experienced professional singer such as Jones. The choir's mastery of these challenges was wonderful to see and hear, and I cannot imagine the composer's vision better realised.

"There will always be a need for Requiems," Gabriel Jackson has written; "for we will always need to mourn, to memorialize, and to be granted some brief glimpse of a better world. And there will always be a need for new Requiems, to reflect our ever-evolving understanding of the world and our place in it, and of the meaning of loss."

Rather in the manner of Benjamin Britten in A War Requiem, but on a very different scale, Jackson places between the liturgical sections prose and poetry by the Australian Aboriginal poet Kevin Gilbert, the 16th-century Japanese Samurai warrior Hōjō Ujimasa - his poem "Autumn Wind of Eve", with its wonderful verse: "Now we disappear,/ well, what must we think of it?/ From the sky we came./ Now we may go back again,/ That's at least one point of view" - and Walt Whitman's "Come lovely and everlasting death". Tagore's "Peace, my heart", and the Mohican chief Aupumut (not Aupumunt, as in the programme), spoken not sung, ending: "Sing your death song, and die like a hero going home".

The overall title of the concert was "O Radiant Dawn" - and MacMillan's piece of the same name opened the programme, radiant indeed, like sunshine. Then camehis Miserere, incorporating thesame plainsong as Allegri does inhis famous setting of these words from Psalm 51. MacMillan runs a church choir in Scotland. He understands.

Before we heard the Palestrina Stabat Mater, there was some piano music - unspecified in the programme, but recognised as the first of Brahms's Three Intermezzi - the one in E-flat major. It was rather incongruous in a programme of unaccompanied choral music and, it has to be said, rather pointless, other than to show that Jones plays the piano very nicely. His announcement was barely audible from my seat near the back.

The same can be said for the talk on the history of the church which delayed the start of the music by some 12 minutes. The speaker clearly knew what he was talking about, with a very engaging manner, undoubtedly interesting, and apparently amusing, judging by the occasional laughter from audience members near the front, but he was inaudible to the rest of us. There appears to be a sound system, but it wasn't used.

For unamplified speech, the acoustics are dreadful, but for music they are superb, allowing clarity and impact - cushioned on air almost - that suits this choir well. It would be good for recordings, if not already used for that purpose. And the choir has some very well-produced voices: the baritone and (particularly) soprano soloists in the Sanctus and Benedictus of the Jackson Requiem were particularly impressive. But all sing with commitment and passion, because they clearly believe in the music and know it well. A whole evening of unaccompanied music of considerable complexity was delivered with panache and elegance.