The CRB check taken by ACO personel is very very through, and as others have said takes months, sometimes more than a year if you are really unlucky!
I have this clearance, and just started a job with a large company. they having nothing to do with young people, but require a CRB check. This is due back tomorrow, and I applied last thursday. My ACO CRB check didnt count because it was for a different purpose.
Funny system - CRB doesnt apply in Northern Ireland, why bother!