Every company needs to maintain a registered office, even those that are dormant or are currently not trading, so that Companies House and HMRC can send their official correspondence. 

Trading includes buying, selling, renting property, advertising, employing someone or getting interest. HMRC has detailed guidance on what counts as dormant for Corporation Tax

If you are registered for VAT and the company becomes dormant, you must deregister for VAT within 30 days. If it is a temporary state of dormancy, you still need to submit "nil" (empty) VAT returns.

You will still need to complete the annual confirmation statement and file "dormant accounts".

You run the risk of being removed from the Companies House register and further action being taken against the company or Directors if you ignore their correspondence.

A Dormant Company does not have to display their Company Name at the Registered Office Address.