Not quite so, Peter.
Employers and voluntary organisations cannot simply choose to ask for a DBS check on a whim. I believe that a number of them are asking for DBS checks unnecessarily. The criteria for the requirement has been tightened and is now thus:
Standard checks – To be eligible for a standard level DBS check, the position must be included in the Rehabilitation of Offenders Act (ROA) 1974 (Exceptions) Order 1975.
These are positions which, if applied for, requires the applicant to disclose convictions which are “spent” under the ROA. The full guidance can be found here:
http://www.hrbc.co.uk/crb-eligibility-criteria-2
But to save you wading through it, working in a charity shop is specifically mentioned:
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Volunteer in a Charity shop
Although the function of the shop may be to provide financial support to a charity which may help children or some vulnerable adults, there is no requirement for people working in the shop to be DBS checked. Although children may come into the shop, any contact is incidental as with any merchandising outlet. Additionally, although a shop assistant may be dealing with money, unless they are working in a position which is regulated by The Financial Services Authority (FSA), they are not eligible for a DBS check.
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I believe that not only are these organisations making themselves look ridiculous by insisting on unnecessary checks, but they also face forfeiting the fee payable when they make their application.