While maestro Gergiev and his soloists continued to battle with The Ring on Saturday, the Mariinsky Chorus spent what could have been an evening off singing Russian Orthodox Music with principal chorus master Andrey Petrenko.

For anyone familiar with both, the contrast could not have been greater.

 Instead of the gaudy trappings of Wagner’s excesses (no one who wrote five-hour operas could be accused of modesty) what we heard was unaccompanied religious choral music at its purest and most beguilingly direct.

Rachmaninov’s Vespers (All Night Vigil) was the main work, originally composed for liturgical purposes, but here presented ‘in concert’. Performed without a break the 15 separate pieces conveyed a devotional intensity that became totally compelling as they unfolded.

Apart from individual details – the simple grace of ‘Praise the Lord,’ rainbow-like textures in ‘O radiant light,’ a creamily unruffled ‘Ave Maria,’ – the most noticeable quality was the Chorus’s vocal richness and balance, not just in the loudest passages, when every section could be heard distinctly (how many British choirs can boast an equal number of sopranos and tenors?) without assaulting one’s ears, but in the gentle shaping of final cadences under Petrenko’s understated, quiet direction.

And those inimitable Russian basses (although their bottom B flat was perhaps not quite as resonant as we hoped) and clarion-voiced tenor soloist Alexey Velikanov also made a huge impression, as did mezzo Maria Shuklina, who was heard to even greater effect in a Psalm setting by Chesnokov in the first half of the programme.