Hi paul ,
I had my certificate from the Criminal records bureau.

The police checks that you can get from your local station are different from the CRB checks.
these checks only show up unspent convictions and cautions but none of the extra information that be be revealed by the CRB.

Also note that there are two types of CRB standard and enhanced.

Standard checks are for people working with children or vulnerable adults.
Enhanced checks are for people with far greater degree of contact with children.

The standard check Should do you , but some local authorities and orginisations can ask for a enhanced check.
And they can insist in doing there own checks as well.

CRB website Criminal Records Bureau - Home Page