18 Digit Ref. Number for overseas payers

Hi, I have read on various threads that this number is needed as reference to any overseas payers who wish to pay the shortfall in years of NI contribution and how it is generated : NI number + letters IC + surname and initials. But for me, and maybe some others, I cannot create 18 digits this way as my surname is too short ( 15 digits in total ) and even if I use all the initials of my first and middle names I still only get to 17 digits. Please can you advise on what to do in this instance. Many thanks.

After speaking by telephone to an HMRC admin worker, a few days after posting this, I was advised that the fact I couldn't make the full 18 digits wasn't so important and 15 numbers were even enough, as the NI number at the beginning was the part referenced in enquiries. Please can an admin worker on this forum clarify this for anybody else reading this post with a similar problem. Thanks.

Hi,
We can confirm that as you are paying overseas National Insurance contributions then your ’18 Digit Reference Number’ is:  Your National Insurance Number + IC + Surname + initial.  
If this does not add up to 18 digits then that is fine.
Thank you.

Many thanks for the confirmation.