The requirement for CRB certificates puts off many volunteers and this is harming volunteer organisations (scouts, sports clubs, PTA's etc etc). Anything that reduces the burden would be welcomed by such organisations.
At present every person working or volunteering at an organisation in which they deal with children or vulnerable adults needs a CRB certificate through that organisation. Therefore, somebody undertaking duties for different organisations needs multiple CRB certificates. I have 5, I know people with even more. This is time consuming and costly. If CRB certificates were transferrable this pointless waste would be avoided.