Identify who your users are

Consider who your users are before you start writing. User personas are evidence-based characterisations of the types of people who use the ONS website. They can help you understand who your users are. These can range from expert users to inquiring citizens. 
It can be easy to make assumptions about users that may be wrong. Users will have different levels of knowledge and education, backgrounds and needs from your content. There will also often be other factors that influence their needs and behaviours, such as time constraints or the device they are using.  
Remember that you are not the user. Your stakeholders may not be your primary user or make up the largest part of your audience.