If I fail either the C&G or EAL test, can I sit the test with the other awarding organisation before 12 months?

No. If you fail the C&G test you cannot try the EAL test (or vice versa). Regardless of which test you sat, you will not be able to re-register for another EWA test for 12 months. TESP will keep candidate approved details on record to ensure this does not happen and these are checked again by NET at AM2E gateway.