Back in my day, (March 99), the CPL General Flight Test (skills test) was broken down into 3 parts, Nav, General Handling and Circuits, if you failed one section you had to redo that part. Nav in my case, if you failed 2 or more you had to resit the whole test. If you failed your resit you had to redo the whole test. No doubt the folk at JAR have changed everything, but that was the broad scheme of things.
ps its wasn't cheap, £330 for partial plus aircraft hire, nb this is CPL, not PPL