But in this case the Bulgar boys have a total new identity which will not show a record even if child criminal records are released.
If a CRB check showed their record there would be no point in giving them the new ID ! Their new ID is a total secret no one knows it not even the police, for the police to know would be too much of a risk, you could not be certain that their identity would never be revealed even if someone hacked the police database for example.
There will be at most one or two very senior MI5 officers who know the new ID and they are sworn by the official secrets act never to reveal it. The same people who give Russian spies who turn informer their new IDs to keep the KGB off their trail run the ID service for people like this. Believe me, if the men who used to be the Bulgar boys get a CRB check in their new names it will be clear!