Three Companies House address concepts cause more day-to-day confusion than any other piece of the regime: the registered office, the director service address, and the Single Alternative Inspection Location (SAIL). They overlap in some ways, are public in different ways, and have changed in important ways under ECCTA. The post-2024 picture is worth getting precise about, because the cost of getting any one of them wrong has gone up.
Registered office: what it actually is now
The registered office is the legal address of the company. It is where official correspondence is delivered, where statutory registers must be available for inspection (or where SAIL notice has been filed), and where formal communications from Companies House, HMRC and the courts will land. Since ECCTA took effect, the registered office must be an appropriate address - meaning the company must be able to demonstrate that documents delivered there will come to the attention of someone acting for the company, and that delivery can be acknowledged with evidence.
PO Box addresses are no longer acceptable as registered offices. Companies House can change the registered office to its own default address if it considers the registered address is not appropriate, leaving the company without a functioning legal address until it provides a valid one. That is a serious enforcement step and is being used in practice.
Director service address: what it does and does not do
Every director must provide a service address - a public address where service of documents on them in their capacity as director is effective. Crucially, the service address is separate from the director's usual residential address, which must also be filed with Companies House but is not publicly displayed (subject to limited exceptions).
Most directors use the company's registered office as their service address. That is operationally simple but means anyone searching the public register sees the firm's or client's business address against the director's name. For directors who want stronger separation from a residential link, the service address can be the firm's own address (where the firm offers a service-address service) or any other valid commercial address.
SAIL: when and why
The SAIL is an alternative location where statutory registers and certain company records can be kept and inspected, instead of at the registered office. It must be filed with Companies House on form AD02 and the company records held there must be specified. The SAIL is public.
In practice, SAIL is used by firms acting as company secretaries who hold statutory registers electronically or at the firm's offices rather than at the client's trading address. It is also used by groups where statutory registers are centralised at a head-office address that is not the registered office of each subsidiary. Most owner-managed companies do not need a SAIL.
The quick-reference for which address is which
When clients ask, this is the simplest way to explain it.
- Registered office: the legal address of the company, public, must be appropriate, where Companies House sends formal correspondence
- Service address (director): the public address for serving documents on each director
- Usual residential address (director): private filing with Companies House, not on the public register
- SAIL: optional alternative location for inspection of certain statutory records
- Registered email: not public, where Companies House sends e-correspondence - required since 2024
How ECCTA tightened the rules
Three ECCTA changes matter most for addresses. First: the appropriate-address test for registered offices replaced the old "any address" approach. Second: Companies House now has the power to query and override addresses that look fraudulent or unused. Third: directors' residential addresses can be suppressed from the public register on application in qualifying cases, but only with evidence of a serious risk (domestic abuse, threats). The bar is higher than the previous Section 243 application route in some respects.
The address-as-service workflow inside a firm
Many UK practices offer a registered-office service, a service-address service, or both, as an add-on for owner-managed clients. The economics are straightforward - a typical price is £80-£200 per year per address. The operational cost is the inbound-post workflow: scan, log, route to the engagement team, and respond inside the relevant statutory window.
Accupe's Companies House sync pulls each client's registered office, SAIL, and registered email into the client record, so the firm can see at a glance which clients use the firm's address vs their own. Compliance Radar flags clients whose registered details look high-risk under the appropriate-address test (PO Boxes, residential addresses that may not be monitored), so the firm can recommend a change before Companies House does it for them.
What to put in the engagement letter
If the firm provides any address service, the engagement letter must specify which addresses are provided, what the firm's SLA is for handling inbound correspondence at those addresses, and what happens at the end of the engagement. A common failure is the client moving accountants and the previous firm leaving the registered office unchanged for months - the new firm then takes on a client whose registered office still belongs to the previous firm. Build offboarding into the contract from day one.
Closing
Addresses are unglamorous. They are also where ECCTA enforcement is most visible, because they are the easiest signal of a passive or fraudulent company. Get the registered office right (appropriate, monitored, with a documented SLA), get the service addresses right (separated from residential where the director wants that), and use the SAIL only where it actually solves a problem. Then revisit the whole picture every year at the confirmation statement - because addresses drift, and drift is what enforcement notices the fastest.