Contract of services review /Annuity purcahse agreement

General information for the business: An umbrella company has given me a contract of services Legal topic: Tax Description of legal work: I am a contractor/interim worker who has joined an umbrella company the umbrella company who will be paying my remuneration. I have been given a contract of services by the Umbrella company in which they have suggested the best remuneration scheme for me for tax purposes. I want to understand what responsibilities it places on me and what responsibilities are on the umbrella company and whether the scheme is legal for tax purposes. Extra notes: