An employer with 5 or more employees must have a written statement of its health and safety policy, with the organisation and arrangements for carrying it out, bring it to employees' attention and revise it as often as needed.
You must also record the significant findings of your risk assessment and any group of employees it identifies as especially at risk. Prepare both before you take on your fifth employee.
Manage workplace risk assessments under MHSW 1999
How to carry out, record and review risk assessments as your business and its hazards change.