Hypothetical of course; I don’t have a CPC, have sort of retired (or having a few gap years) But doing a lot of cycling. Now sometimes I get a lift off a mate 40 or 50 miles into the wind then have an easy ride back (its a wonderful way to go cycling). Now if my mate got me to drive (using my drivers card) so he could have an hour off. Would I be breaking any rules under the CPC laws - The truck is working (although running back empty) but as I’m not getting paid I would hardly be doing it professionally.
I would say that you would be breaking the law as the vehicle is used for hire and reward also you are not employed by your mate so their is the question of insurance.
Dont think theres an opt out for CPC old chap !
I like taking train and riding back . have to wait til rush hour over and hope that theres not 2 other cyclists already on board !
Until recently was 22 miles to train station , but now im near 1 is quite fun day out
The Vehicle is for commercial use on the Road.
If you were moving your Privat Stuff,you could put Tacho Out of Scope,and,well,…
Company would also have missed Milage in there records and may think your Friend drives with Card in second Slote
Seeing as this isn’t a real situation and just hypothetical - stick some L plates on and claim your are undergoing driver training which is exempt DCPC.
On the other hand - don’t be silly 
If caught without the DQC it can be a trip to court. Pay the £300 or so for 35 hours ‘training’ and get a DQC … you know you want to
Not DCPC related, but in your scenario you’d effectively be double manning with your mate, so you’d need to ensure that your card was in the head within an hour of him inserting his.
I may be wrong of course having never double manned it’s not something I’m completely up to speed with.
Comparable scenario - If during the course of his working day, your buddy picked up a hitchhiker, would it be ok for the hitchhiker to drive for a bit without a current cpc? I dont see how his driver card would be fully legit anyway without his 35 hours tagged on, so would think that unless he had all the relevant, up to date ■■■■■■■■ that the powers demand of him, hed be out on a limb. Aside from all that, the company insurance would be void in most, if not all instances of this kind.
He’s an owner driver and his insurance would def cover me if I was working for him or for instance taking a trailer in for plating. But I largely agree with some of the above that if the truck is actually working then I shouldn’t be driving it. Even if I am not getting paid with money I suppose the argument could be I am being paid in kind with the reward being the lift.
Didn’t know about the double manning stuff with card needing to be inserted within an hour - I think he is just wanting to take his break with his truck moving, so there is another argument for me to say NO with.