Companies House's online filing system can't process a straight name swap between two companies, because it validates that a new name isn't already in use — and each company's desired name is currently held by the other.

The only way to do this is by paper filing, using two NM01 forms and a covering letter explaining the swap:

1. Complete an NM01 for Company A, changing its name to Company B's current name.
2. Complete a second NM01 for Company B, changing its name to Company A's current name.
3. Include a covering letter explaining that this is a name swap between the two companies, so Companies House can process them together.
4. Enclose a cheque for £30 per form (£60 total for both), made payable to "Companies House."
5. Post both forms and the covering letter to:
   Companies House
   Crown Way
   Cardiff
   CF14 3UZ

Because this is a paper filing, it will take longer to process than an online submission — build this into your timeline.