my current workaround (which I'm somewhat uncomfortable with) requires an assign statement in those BPLs which reference the rules:

set context.HL7 = request

Thanks Shamus, I have tried Document.{etc} and get the same error as for HL7.{etc} :

ERROR <Ens>ErrException: <PROPERTY DOES NOT EXIST>zevaluateRuleDefinition+26 ^ full name of rule class.1 *Document, etc etc

Thanks Jeffrey, these general business rules are to be used from a couple of BPLs, I already have the other actions and routing happening in these BPLs, it's just a case of getting the shared rules to inspect HL7