What is the military equivelent of a criminal records check?

I need a document stating that I have no criminal record for a visit to the UK to work with children in a school. They have CRB (criminal record bureau) checks over there to work with childern. I am active army. What kind of (official) document can I show them, (which I could already have or wouldn't be too hard to get hold of), that shows I have no criminal record? Thanks in advance!