A document may be served on a company registered in the UK by leaving it at, or sending it by post to, the company's registered office — section 1139(1) of the Companies Act 2006. For a claim form, CPR 6.9 also permits the company's principal office, or any place of business with a real connection to the claim.
Where personal service is required or preferred, the document must be left with a person holding a senior position — a director, secretary, treasurer, chief executive, manager or other officer of the company (Practice Direction 6A, paragraph 6.2). Service is then proved by a certificate of service under CPR 6.17.