Outline Partnership Agreement from the Charity Commission. This Guide is not intended to be a precedent or definitive model agreement, but a guide and check-list. Every project and partnership will be different, and the content of the agreement will vary according to the particular situation. Legal advice in preparing the agreement, or reviewing it, is highly recommended,particularly where there is a significant level of funding, or where reputational risk is at stake.
Tools4Dev have an example Memorandum of Understanding between two charities working together.