I've found the linkedIssues() function, but it requires an issue key i.e. it's limited to finding all linked issues of type X to a specific issue. You don't appear to be able to wildcard it in any way. e.g issues in linkedIssues("BT-1","is duplicated by") works happily, but only for the root issue "BT-1".
I want to be able to generate a list of all issues having a linked issue where the link type is, say, "is duplicated by".