"Strengthening Democracy: Fair and Sustainable Funding of Political Parties" by Sir Hayden Phillips sets out a range of reforms. An increase in public funding of political parties to enhance public engagement, recommendations on limiting donations, limits on spending, public funding and regulation. There will have to an acceptance in part or full by the major UK political parties.
In respect to the Co-operative Party, it gets a little footnote on Page 10 (30 pages in total) "It is owned by the Co-operative Societies which are, in turn, owned by their individual members, and the Party receives its funding from them. The payments are made by the Societies acting together, but they are an expression of the views of individual members. I do not think it appropriate that these payments should be caught by a cap."
You can plough through the download document (PDF) at Party Funding Review or just look at the recommendations on one page.