If the aircraft is used for CPL skill tests or initial IRs then the checklist needs to be approved by a CAA Flight Examiner along with the whole aircraft. If the aircraft is used for multi-engine, type or instructor training then the checklist should form part of the operations manual and should therefore be approved by a CAA training standards inspector. If it's just PPL/IMC work then the PPL examiner effectively approves or rejects the checklist when he does a test. Generally speaking the checklist should have a minimum of all of the checks that are in the POH. Things like pre-takeoff and descent checks can be added to and massaged into mnemonics but, unless there's a very good reason for it, and your insurers agree, emergency drills should be exactly as is.