Hi Paul welcome to the site...
to "Calculate" your radio code we'd need the 10 digit part number as well as the serial number beginning
BP (that you've already provided
)
I have downloaded an app that can do this in a jiffy
I've had a look in my Micra Owners Manual (that came with the car) and it explains how to enter the code...as follows :
To unlock the unit, enter your 4 digit radio code. The code is entered by using the preset station buttons
for example: if your code is say... 4321...
you'd press the
(1) button four times,
then the
(2) button three times,
the
(3) button two times
and the
(4) button once...
then press the
TA button to confirm the code.
If the code is
correct the unit will switch on.
if the code is
incorrect the display will say "Error" followed by "wait 1 hr" and by wait one hour it means have the unit "on" for an hour...
I can only assume that if you switch it of then on again before this hour is up it will ask you to wait another hour <_<
I hope that helps ...a bit ^_^