Mr Ferry..I hope this helps...
1 If you are quite certain that you committed no offence, do not, under any circumstances admit that there was a possibilty of an offence being committed. Don't even consider doing that because it will certainly jeopardise your defence in the event of court action.
2 Remember that the CAA only ever pursue legal-action where there is a strong chance of a successful prosecution.
3 The CAA are totally mindful that many compalints are groundless/scurrilous/mischievous. They are also quite aware that even sincere complainants are (usually) hopeless at estimating heights.
4 If you are interviewed in person, note that the CAA interviewer will be a former police-officer and NOT an aviation expert. His skills will be confined to interpreting the law and interview procedures.. he/she will most likely have no flying experience or qualifications.
5 Previous advice about consulting BALPA and/or a specialist aviation lawyer is good advice.
Good Luck BM