In July the pair will unveil firm proposals for lenders demanding a ‘common approach’ to charging fees.
Paul Smee, CML director general, said: "This collaboration with Which? has helped lenders focus on practical and simple ways to help customers by making information more transparent and consistent.
“We hope customers themselves will find it easier and less daunting to make informed choices about their mortgages as a result."
The pair are proposing that different lenders use consistent wording when charging fees, while they should explain when fees are compulsory or unavoidable and when they will be charged.
The CML and Which? also said borrowers need to have a clear idea of how much mortgages will cost over a period of the loan, rather than focusing on just up-front costs.
Richard Lloyd, Which? executive director, said: "Which? has been working with the CML to simplify the wide range of complicated fees and charges in the market so people don't pay over the odds on their loan.
“We look forward to all mortgage providers making these changes so that people can get the best deals more easily."