I feel a rant coming on - but that will be another thread.
FP - the scenario of the CPL flight test is that you already hold a CPL and that this will be "a simulated public transport flight conducted in accordance with VFR flight rules".
To operate a "public transport" flight you must have an AOC (Air Operators Certificate), to get one of those your company must have an Operations Manual.
As a pilot with that operator you must abide by that manual and comply with all its rules and regulations - some of which are law, some of which are company mandated.
One of the sections of that manual will be the "Official Company Flight Log(s)" - both VFR and IFR.
The flight school that you choose - OAT in this case - will have "Company Approved Flight Logs" and the CAA Examiners based at Oxford are well aware of that - indeed, one of them may well have written the thing. If you attempt to use any other log (of your own construction - or copied from fellow pilots) be prepared to answer questions as to why you are not complying with the Company Operations Manual.