Late Proms can sometimes outstay their welcome. But there was never a danger of that with the Estonian Philharmonic Chamber Choir’s rich and reverberant rendering of Rachmaninov’s unaccompanied Vespers of 1915 under Paul Hillier. Performances of this All-Night Vigil in 14 episodes can sometimes wallow in the Slavic sonorities of Rachmaninov’s dazzlingly complex vocal writing so much that the work loses its momentum. But Hillier gave the Vespers liturgical and musical direction, while allowing full range to its unique choral colours and contrasts, in which some eye-wateringly low bass singing stood out.