The P11D(b) is included in the XML file submitted to HMRC as part of your End of Year Filing. Please see illustrative file constructed for submission below:
Sample XML File for End of Year Submission
This means HMRC have the full information for your return, unless you have more than the submission limit for items like Cars (50 records for an individual) and Loans (10 records for an individual), in which case you will need to use the traditional paper P11D(b) and also produce an amended P11D for those people being affected.
Otherwise, you will need to simply arrange payment of Class 1A NICs. Further information on paying this can be found on the Government Site here.