Yes. Under section 1139(1) of the Companies Act 2006, service at the company's registered office is valid even where the company does not trade from there. A registered office that is a serviced office, a mailbox or an accountant's address is still the company's official statutory address, and a document left there or posted there is validly served.
The practical question is who accepts the documents and in what capacity. Where the address refuses or has been abandoned, we record the evidence and report it so an application under CPR 6.15 for alternative service can be made on real facts.