The moment an applicant unconditionally accepts your offer of a job, a contract of employment comes into existence. The terms of the contract can be oral, written, implied or a mixture of all three.
Even if you do not issue a written contract, you are under a legal duty to provide all employees who will be employed with you for one month or more with a written statement of main employment particulars within two months of the start of their employment with you. If you have an employee who is going to work abroad for more than a month within two months of starting work, you must give them their written statement before they leave.
The written statement is not itself the contract but it can provide evidence of the terms and conditions of employment between you and the employee if there is a dispute later on.
This guide lays out your legal obligations when issuing a contract of employment or a written statement.