I would like to express my heartfelt gratitude to my principal supervisor Dr Philip Cashian for his truly inspirational teaching, support and guidance throughout the four-year period of this research, and during the preceding preparation and application. I would not have even commenced this doctorate if it was not for his vision, encouragement and expert advice guiding me.

I extend my thanks to Sir Peter Maxwell Davies, Julian Anderson, Sir Harrison Birtwistle, Simon Bainbridge, Brian Elias, Michael Zev Gordon and Colin Mathews for their inspirational tutorials, advice and recommendations during this period.

Heartfelt gratitude I express to the memory of the late Prof. Dr. Elena Toncheva. I could never forget her enlightening and profound contribution to my work and this research. Her expert guidance in the field of medieval chant was a true revelation to me and her help was invaluable. Heartfelt thanks also to Assen Atanasov for his impressively knowledgeable and greatly relevant guidance and information within that field.

I am ever so grateful to Dr Neil Heyde for his very important guidance and advice throughout the process and up to the very last stages of revision and editing; to Dr Raymond Holden for his greatly influential and ever positive and enthusiastic support; to Dr Sarah Callis and Dr David Gorton for their academic support and to Roger Barnes for his important help with editing the text.

Huge thanks to the Harold Hyam Wingate Foundation, Alan & Nesta Ferguson Charitable Trust and Sir Richard Stapley Educational Trust for their generous financial support through grants and scholarships which made all this possible, and to the Royal Academy of Music and particularly the Research Department for their substantial support by appointing me on a Research Internship from 2008 to 2011.

I am extremely thankful to my wonderful family for their unfailing support, love and encouragement, to Mr I.D. Cramer for his truly indispensable support and friendship, to my dearest friends: librettist Marike van Aerde and conductor Jessica Cottis, for their invaluable contributions to my music, research and life in general in this period, to all my friends, who are some of the greatest supporters of my music, and particularly to Yordan Kamdzhalov, Anna Chobanova, Scott Lygate, Ivo and Vania Stankov, Martine and Pierre Vigier, Achim Holub, Christian Ludwig, Robert Tuohy, Steve Todorov, Patrick Nunn and my friends from the St Albans Evening Rehearsal orchestra, whose various contributions to my work and activity have made this effort fruitful.

Huge thanks to all performers who have taken part in premiering and performing the works in this thesis and featuring in the recordings: conductors Michel Tabachnik, Franck Ollu, Keith Bragg and Fabien Gabel; percussionists Tatiana Koleva and Sarah Cresswell, soprano Clarissa Miller, basses Frederick Long and Marcin Gesla, violinists Helena Nicholls and Carolyn Stuart; pianists Svetozar Ivanov, Raya Kostova-Humphreys and Charlene Farrugia; the Azalea Ensemble, Stankov Ensemble, Forte Quartet, String Quartet “Frosch”, Brussels Philharmonic, Varna State Opera Symphony Orchestra and all my friends and colleagues who have taken part in performances of my works as members of the Royal Academy Concert Orchestra, RAM Festival Orchestra, RAM Symphonic Wind, the Manson Ensemble and all other performances involving Royal Academy students and alumni.

Heartfelt thanks to HoneyRock and Richard K. LeVan  for publishing Apocalyptic Passacaglia, Gilles Ledure and Caline Yamakawa from the TACTUS Young Composers’ Forum, Jean-Paul Dessy for his honest and influential support, Claude Ledoux and Ars Musica International Music Festival, Belgium; Ann McKay and the BBC Symphony Orchestra, the Municipality of the City of Varna, Penka Zhivkova, Zhana Andreeva, Stanka Dimitrova, Panko Anchev, Daniela Dimova and the Varna State Opera; Maria Kondova and Elite Music, Pentcho Pentchev and the PENDIM International Competition for Percussion, Bulgaria, the Bulgarian National Radio and everyone there who have supported my work, Nicole Rochman and Sound and Music, David Knotts, Julian West and Kate Denes from Open Academy at RAM; Rosemary Blakesley and the Ashover Festival, Silvia Tihova, and everyone else involved in commissioning my works during this research or organising premieres, recordings and performances of these works and/or supporting my development as a composer and conductor.

Heartfelt thanks to the late Sir Charles Mackerras, to Lady Valerie Solti and to Andrew Ritchie CBE for their support as patrons for the premiere of The Mirror.

I am very grateful to the Royal Academy of Music for providing a great environment and support for this work, to all members of the Academy who have supported my work and particularly to Professor Jonathan Freeman-Attwood, Timothy Jones, Jo Cole, David Pettit, Nicola Mutton, Philip White, Helen Wills, Liz Williams, Hannah Melvin-Smith, Fiona Hymns, Antonia White, Rob Wilding, Janet Snowman, Claire Watts and all the librarians.

Many thanks to Kirsten Cowie who has produced and engineered many of the recordings in this portfolio, to producers Liudmila Gerova and Lili Nikolova from the Bulgarian National Radio and to all other producers and sound engineers who have worked on the recordings in this thesis and some of whom I might have not met, but whose contributions I highly value and appreciate.

Huge thanks to all my professors and teachers who have taught me for the music degrees preceding the current doctorate, as their contributions have naturally played a significant role in it indirectly. Particular thanks to Prof. Vassil Kazandjiev, Colin Metters, Sir Colin Davis, George Hurst, Prof. Plamen Djouroff, Prof. Milko Kolarov, Prof. Tatiana Karparova, Prof. Krassimir Taskov, Dalila Nedelcheva, and also to everyone who provided scholarships and support for these previous degrees.

Many thanks to all whom I have not succeeded to mention here, but who have contributed to this research and to my work as a composer and conductor. The work presented here is a great team effort and the scale of support and help that I received for this work only humbles me. I feel that the credit I receive as a composer is not at all proportionate to my humble contribution to this huge team effort.

I thank Father Vasiliy, Father Hristo; Father Simeon and Lotthen Presbyter, for their spiritual support and guidance, and to my godfather Leonid and his family.

I thank our Lord for his great mercy and love to me, the unworthy.