Unfortunately it will never be removed from the police database. It will come up if he has to do an enhanced CRB check, but that is only for teachers, policemen, positions in national security and high positions in financial institutions. It will not come up on a standard CRB and obviously does not count as a criminal record.
If I was him I would make a counter-accusation of attempting to pervert the court of justice against the person who made the false claim against your son.