Sending paper documents to HMRC via registered/tracked mail

Hello :) For various reasons, I am required to send paper registration forms to HMRC to register a new parternship. In the past, such forms have been lost in the post and we would like to send them using a trackable service. The BX9 postcode isn't recognised for these services - is there an alternative address I can use please? Thanks

Hi,
The address to submit the SA400 is:
HM Revenue and Customs,
National Insurance Contributions and Employer Office,
BX9 1AN
Thank you.