Phone the CAA and speak to one of the aeromedical advisors. They answered all my questions and were very helpful, offering advice and suggestions on things to do before taking the medical. This was for the class 1. Explain to them, as you have done here, your circumstances and they will tell you whether it is considered as a significant admission or not.
It would be worth your while going straight for the class 1 if you intend to go onto the CPL/IR as without this you won't be going anywhere in a commercial sense. If you did fail the class 1 (hopefully not) then a class 2 may still be issued if you meet those requirements.