You will find a good discussion of this issue in part II of the English Law Commission Consultation Paper 175, “Capital and Income in Trusts” http://www.lawcom.gov.uk/wp-content/uploads/2015/03/cp175_Capital_and_Income_in_Trusts_Consultation.pdf (2004). (The subsequent report (Law Com 315, 2009) contains a shorter summary discussion, so you want to look at the consultation paper rather than the final report.)
James Kessler QC
15 Old Square
Lincoln’s Inn