CRB checking silliness

I saw my dad at the weekend (went for geeky day out for his birthday, and thanks to people who suggested Kew Bridge Steam Museum).

Apparently Harrow Council has a (daftly named) "Neighbourhood Champion" scheme, and had suggested that he might be interested (he's involved in a local residents' group). He refused on the basis that he could see nothing in the remit of the role that justified Harrow's requirement for CRB screening — indeed as far as I can see the role doesn't involve anything that any member of the public can't do anyway.

Does anyone know if there is a specific reason for this, or if it's just Harrow (or the Met?) being overzealous in arse-covering?