Yes guys, it's absolutely fine. I got my initial Class 1 before starting the CPL ground exams, just to make sure I could get one. I let it lapse for about a year, and had to get it back before I could apply for my CPL(H). I did that through my AME; no problem at all. I'm now flying on a class 2 again, as I haven't got a job yet. I'm not certain how long you can let it lapse for, but I'm about to check that out in the next month or so when I renew my Class 2.