The simple answer is yes. Firstly, it avoids dispute later if terms between the parties are recorded in writing. It is much clearer than having an oral agreement which can be questioned later. It is also a legal requirement that all employees are given certain information as set out in s1 of the Employment Rights Act 1996 within two months of starting employment. If you are not sure what must be recorded in writing for the contract to be s1 compliant you can find this information in my useful resources section.