Government Digital Service (GDS) have created and maintain a service called the GOV.UK Design System. It is a set of styles, components and patterns that make UK Government services look like GOV.UK. The code for the styles, components, and patterns is stored in the GOV.UK Frontend repository and is all open source and is free to examine and use.
We as a department encourage all government departments to use it, but we can’t enforce it. As every department is essentially its own separate entity, we have very little visibility on who is actually using it and where it is being used (unless they approach us for support leave us feedback). This creates problems when we are asked to provide numbers on the adoption across both central government services, and more recently local councils too.
Opening this thread to continue the discussion and analysis.