Contracts are an essential part of every freelancer's toolkit and should not be underestimated. Not only do they outline the wants, needs and expectations of the parties, but they also provide a legal framework within which these will be achieved, and a back up should legal intervention be required. Contracts provide a formal definition of the business relationship between the freelancer and agency or direct client.
You need to agree with your client whether you are being taken on as a temporary employee or a contractor. If your client will control you closely, guarantee to pay you whether or not there is work to do and not allow you to send a substitute if you are ill or unable to come in to work, then you will be probably be hired as an employee on a fixed or short-term contract of employment. You can then accrue employment rights from day one.
Working through an agency Directly engaging with a client Confidentiality agreement Director's personal guarantee to the end client What makes a good contract? Tax and contract helpline for IPSE members Contracts: What you need to know Letters of Engagement