People are getting quite wound up on here about logging illegal flights.
You can put whatever you want in your logbook, you could log passenger time in the back of an Easyjet for all it matters, what is relevant is what you are submitting to the authority when applying for a licence.
If you are trying to use hours flown illegally (ie no insurance, stolen aircraft, no ARC, whatever) to obtain a CPL(A), do you think the CAA will issue the licence?
Once pilots have their final licence, they may never send their logbooks off again, if PPL(A) is all you'll achieve, then you could fill your book with illegal fights and unless you happen to get checked by an examiner or audited for some reason, then noone is any the wiser.
Once you submit it for a CPL application, it will be scrutinised, and if there is an audit with no paper trail that you were actually PIC on a legal flight which you are trying to claim towards the CPL requirements, some difficult questions will be asked.