Millett was also notable for his contribution to the law of equity and trusts. He wrote the leading judgment in Foskett v McKeown, a landmark case on the English law of trusts, concerning tracing and the availability of proprietary relief following a breach of trust. He also decided Bristol and West Building Society v Mothew, a leading English fiduciary law and professional negligence case, concerning a solicitor's duty of care and skill, and the nature of fiduciary duties. The case is globally cited for its definition of a fiduciary and the circumstances in which a fiduciary relationship arises.
