As an employment lawyer, a written contract does not have to be in place by law but an employee is entitled to a statement of terms and conditions which must include the minimum requirements under the Employment Rights Act 1996. This is what Antonia is referring to.
A contract can be created in many ways, including verbal, written, conduct and performance. If the statement of terms and conditions as mentioned above is signed by the employer it is likely to be strong evidence of a contract.
Jonathan