Where do I send a formal letter to a limited company, and how do I prove it arrived?
The short answer
Its registered office. The Companies Act 2006 says a document may be served on a company by leaving it at, or posting it to, that address1, and since 4 March 2024 it has had to be an address where a letter would reach someone acting for the company and delivery can be recorded2. Post the letter there with a signature on delivery, email the person you deal with, and keep both records. An address on the invoice, the website or an email signature is not the registered office unless the register says so.
England and Wales only. WolfX is software, not a law firm.
What you can add
A £6,800 invoice, letter posted 13 October
Say you invoiced another business £6,800, due on Friday 14 August 2026. On Tuesday 13 October you post a letter to its registered office with a signature on delivery, and email it the same day. By the court's yardstick the email counts that day and the post on Thursday 15 October. The 14 days run from sending and end on Tuesday 27 October: 74 days after the due date. The invoice went late in the second half of 2026, so the rate is 11.75%10: 8% plus the base rate9. Postage is left out.
Then it grows by £2.19 a day until they pay. If it is still unpaid, a claim for about £7,032 costs a £455 court fee12.
The road ahead
Five steps. Postage is the only cost.
Step 2: Post it to the registered office
Address it to the company by its exact registered name and post it to that address with a signature on delivery, or take it by hand with a witness. A director's home is the wrong address: the debt is the company's.
The pre-action rules8 say you write to the other side but not how, so the registered office is the address least open to argument.
Step 3: Email it the same day
Send the cover note below, with the letter attached, to the person you dealt with and to the finance contact. An email shows when you sent it, not that anyone opened it, so don't rely on a read receipt.
Step 4: Keep the record
Keep a copy of exactly what you sent, the postage receipt and the signature record. By hand, note who, when, where and to whom, and photograph the letter in place. GOV.UK's records for serving a statutory demand7 are the pattern.
Add one line to the file: what, to where, how, when, by whom, and where the proof is.
Step 5: Know when it counts as delivered
Posted to the registered office, it counts as delivered when the post normally would, unless they prove otherwise5. For a date, use the court's yardstick: first class post, two days later if a business day, otherwise the next; by hand or email before 4.30pm on a business day, that day6.
Give them 14 days from the day you send it, and write the same date in the letter and the email. 14 days is what the court treats as reasonable8 in a straightforward case, and how long to give them has the rest.
A letter you can copy
Cover email for the posted letter
Send it the day you post a letter before action or a final demand, with a copy of that letter attached.
Tap a highlighted gap to see what goes in it.
Send it from your own email, so the sent copy carries the date, time and attachment, and keep it with the postage receipt. The signed delivery record is the proof. The email is the back-up.
When not to bother
When it isn't worth it
- They're a sole trader or an ordinary partnership. Neither has a registered office: send it to where they trade, and see the debt protocol for a sole trader. An LLP has one; treat it like a company.
- It's dissolved, in liquidation or in administration. A letter is the wrong tool. Start with checking its status.
- The register shows a default address. The registrar can nominate one, and it need not be an appropriate address2, so a letter posted there may reach no one. Post there as well, and email the people you dealt with.
- It's a statutory demand. That is left at the registered office or handed to a director7, with post only as a fallback. The statutory demand page has the rest.
- It's a plain reminder. An email is enough until you reach the formal letter.
The Wolf's note
The register decides the address, not the invoice. Post to it, email the people you deal with, and write the date down the day you send. Then 'it didn't arrive' has a signature to get past.
Mr. Wolf · the AI inside WolfX
What comes next
Your next move
What is a letter before action, and how do I write one?
A formal last letter before a court claim, and you can write it yourself.
7 min read · Letter included
What is a final demand letter, and when do I send one?
Not a legal term: a firm letter with the sum and a pay-by date.
6 min read · Letter included
What is a statutory demand, and when should I use one?
Only for debts nobody disputes.
6 min read · Letter included
Don't want to do this yourself?
The Wolf does every step for you. He works out the sums, writes the letters and keeps track of every date. Nothing goes without your yes.