The eight (!) previously unrecorded works presented on this disc span the length of Britten’s career. Two come from 1930, when he was 16 and newly enrolled at the Royal College of Music: a three-minute sliver of a piece for string orchestra and two unfinished yet far more substantive movements of a Rondo concertante for piano and strings (the latter’s loose ends have been handsomely sewn up by Colin Matthews). Both fragments are finely textured, harmonically adventurous and assured, and full of striking ideas.

Les illuminations (1939 40) is quite well known, of course. But here, in addition to the song-cycle, we have three songs (in Matthews’s orchestration) discarded from the published version. “Phrase” is extremely brief and has a prefatory, recitative-like character. In the exquisitely evocative “Aube”, however, Britten magically illustrates one of Rimbaud’s ecstatic visions; why he thought this song to be disposable is beyond me. An intense, almost Mahlerian sense of yearning makes “A une raison” engrossing, too.

Britten began writing a Clarinet Concerto for Benny Goodman in 1941, during his final months in the US. The first movement was complete (in short score) when he returned to the UK in 1942 but the project was abandoned. Matthews has orchestrated this rhythmically playful piece as well as the 1941 Mazurka elegiaca (originally for two pianos), and filled out the sketches for another unfinished work from this same period to create three “Movements for a Clarinet Concerto”. It’s an attractive and sturdy score that brings to light some marvellous music. Indeed, the wave-like passages in the first movement (beginning around 3'00") presage Peter Grimes.

Matthews has also masterfully realised In memoriam Dennis Brain (1958), an anguished, angry and affecting work for four horns and strings. Since Brain, who was killed in a car crash, played a crucial role in the creation of the Serenade (1943), Britten freely quotes the “Lyke-Wake Dirge”, the darkest song from that song-cycle. And, finally – for solo piano – an unfinished set of theme and variations intended for the 1966 Leeds Competition. Improvisatory, ruminative (note the use of repeated notes) and exploratory in its use of extended tonality, it is a small but significant cobblestone in the path towards Britten’s late style.

All the performances are superb. Sandrine Piau’s stylish and imaginative interpretation of Les illuminations is one of the best soprano versions on disc, in fact. Michael Collins’s easy virtuosity in the Clarinet Concerto is a joy. And throughout, Thomas Zehetmair elicits razor-sharp, sensitively shaped playing from the Northern Sinfonia. In short, this is one of the most important Britten recordings in many a year.