For the record CRB checks are not time consuming. There are plenty of companies out there that will do them for a filled form and a £50 (approx.) cheque. A couple of years ago my wife was using a charity that would do it for youth oriented not-for-profits for about £15. I can't recall the name of that charity right now but would be happy to look it up when required.
I did a little research and it looks like we could do it for free. The CRB doesn't charge a fee for volunteers so it's just a matter of finding a handling agent that won't charge a fee, and they seem to exist.