Regardless of whether your company is dormant (not trading), you still have annual requirements that your company must complete as you would do for a fully trading company. You don't have to pay Corporation Tax or send a Tax Return if you're dormant.
Your annual dormant company requirements with Companies House are:
Confirmation Statement - You will need to choose the dormant SIC code (99999)
Dormant Company Accounts - The accounts will be marked as 'nil'
*A special bundle of both of these services can be purchased from any of the above links