Towards the end of the war, William Alwyn was elected to the committee of the Composers’ Section of the Society of Authors. It was initially a frustrating experience. Most of the board members were elderly and pompous, and, according to Alwyn, its chairman ruled out of order everything that could further the cause of British music. So in 1947, with the help of colleagues, Alwyn initiated the Composers’ Guild of Great Britain. Retaining its affiliation to the parent society, the Guild aimed to protect the legal rights of his fellow musicians (in which it hit), and to secure minimal concert performances of British works (in which it missed). Alwyn's election as chairman in 1949 was in the midst of what he called a McCarthyite “witch-hunt”, and the Guild seemed likely to collapse under a threat of mass resignations. Fortunately, the affair calmed down, and Alwyn survived to serve again in 1950 and 1954.

In the same busy period he helped to form the Society for the Promotion of New Music, offering new composers a chance to hear their works in performance - not unlike the New Music Society he had founded in 1932. Committee work did not end there, for he was also elected to the council of the Performing Right Society, a position that led to the Executive Committee and, over the coming years, a number of international conferences.

There were also health worries. For two years doctors had diagnosed a persistent difficulty in swallowing as a “nervous affliction and … treated accordingly in spite of increasing misery and frequent bouts of choking”. Finally, Alwyn explained in his brief autobiography, “an ‘X ray’ revealed a pharyngeal pouch - a lesion of the muscles at the base of the gullet which necessitated a severe operation”. Alwyn entered University College Hospital “calm and resigned, glad to be finished with the fearful years of near suffocation and almost welcoming the knife”.

1949 also saw the completion of his First Symphony, so time must have been severely restricted, yet he managed two feature commissions for this year and five more for release in the first four months of the following year. The 1949 releases were produced by John Mills, the actor's star in the ascendant after Great Expectations (1946), and scripted and directed by Mills's close friend Anthony Pelissier.