The 1980s began auspiciously with a telephone call across the Atlantic from the Boston Symphony Orchestra, requesting that I should compose a work for its Centennial celebrations. Unable to imagine any greater stimulus than to compose for this magnificent American orchestra, I immediately agreed.

Before I could start, I had already on my plate some interesting commitments. Accepting a new commission is always a euphoric experience and I spend happy moments after signing an agreement dreaming of how I can make the most of each particular opportunity. However, I always resist the temptation of tackling the fresh project until any current undertaking is safely completed. I do not like to involve myself with several compositions at once.

So for a long time the promised piece remains a pleasurable future challenge. Then suddenly an alarming moment arrives, when I come face to face with blank manuscript paper, often with a deadline roaring towards me.

That early stage in the creation of a new work is for me the hardest. Everything has to be imagined and worked out in my head before a single note is put on to paper. Here my geometry is a great help, providing as it can an unseen framework around which I can organise my notes, my thoughts and feelings. Sometimes an idea comes at once; sometimes this chrysalis stage takes weeks, even months. I just think and plan, keeping to my daily discipline, going to my studio from nine in the morning till seven in the evening, either sitting silently, or experimenting with new harmonies and new sound combinations at the piano. Most days I continue my efforts as I go for walks along the River Thames, my mind totally abstracted in my search for a new musical architecture and climate, which I try to make different for each successive work. At these times, I am so absorbed in my patterns of emerging sound that, apparently, I stride straight past and stare right through my Twickenham friends and neighbours, who by now understand and do not take offence.

Once the structure of a new work is clear to me – once I know where I am going – I roughly sketch the whole outline in pencil and the first important stage of creative work is over.