Your question was headed notice of intended prosecution which is what I assume you have received. The Police are simply investigating the offence of failing to comply with a road sign at a particular date time and location.
They want you as the registered keeper of the vehicle or as someone they believe may have knowledge of who was driving to tell them who it was
It is an offence not to provide the information requested unless you dont know and cant with reasonable diligence find out who the driver was