Request more information app flow - validation on national identifier

Summary

No validation on national identifier in the RMI workflow

Content

Scenario: As an external candidate, I am asked to provide my DOB and National Identifier (National Insurance Number) in the app flow. However only the DOB is mandatory. 

So we have configured a request more information action that will ask for the National Identifier post offer. The issue we have seen is that unlike in the app flow, the RMI request does not validate the format of the identifier. Therefore it can be keyed in the wrong format by accident, then causing issues when the flow into Core. Is there a way to rectify this?