Class 3 NI: Need to inlclude IC in payment reference if paying from UK bank?

I today received an email from the IPC advising me of the years and amounts of Class 3 contributions I can pay. Wherever I have looked before, including here, the advice has been that the reference to use is your NI number, followed by IC and then surname and initials up to 18 characters. The document INS13 sent by the IPC however states that IC is needed if paying from a non UK bank account and that if paying from a UK account the reference should be NI number followed by surname and initials? Given I want zero risk of payments going astray either by or by not including IC in the reference, which is correct?

Hi Adey,
We can confirm that as you appear to be paying voluntary National Insurance contributions from overseas, the correct format of your ’18 Digit Reference Number’ is:
National Insurance Number followed by IC followed by surname and initials if possible.
This Reference Number is the same whichever bank account you use to make your payment to us.
Thank you.