When you lookup a company on www.companiesintheuk.co.uk you will see the company's registered address.
The registered address is the official legal address of the company. This is the address that official legal notices are will be sent to. So if you have a legal demand for payment, then use the registered address. The registered address is also, typically, the address at which a company is required to keep its company records available for inspection. Company law is complex, you can also specify a different Single Address Inspection Location (SAIL) which overrides the registered address as the locations where the company documents can be inspected.
The registered address is required to be a real physical address, you cannot use a P.O. Box number. This is because in order to serve a document on a company you need a physical location to go to.
The registered address is disclosed on the public register of companies, and freely available. Many companies have no real location, and are based out of the directors residential house. So many companies use a Registered Address Service, which allows them to use the physical address of a third party, who will then forward on mail to the private address. Our website will warn you when it suspects that the registered address is actually a service address on the location tab, as shown below:
Although not an indicator of any fowl play, this should make you question why a company would want to pay a service to obscure it actual address. A question to ask if you are about to do business with the company.