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
You will need to notify HMRC that you are dormant to avoid the requests to submit Tax Returns.