We were asked a couple of years ago to get Safecontractor accreditation for a contract, which I believe is similar to CHAS.
There are a lot of questionnaires to fill out, quite time consuming, however, as long as the contract is worthwhile, it's worth doing, and while it may not help you gain new customers, it will help as a tool to sell your services.
Our Safecontractor pays for itself many times over each year.