Special Public Bill Committees are committees which are empowered to take written and oral evidence on a bill. Following such evidence taking, the Committee is able to amend the bill before reporting it to the House.
Law Commission bills are normally committed to Special Public Bill Committees. This bill, the Trusts (Capital and Income) Bill, was committed on the 10th June.
More information about the bill can be found on the Trusts (Capital and Income) Bill [HL] 2010-12 to 2012-13 bill page.