I think you go along to a Notary Public for a certified copy.
Don't send the PP to the CAA. Recorded Delivery means exactly zilch. It is not tracked and if the package vanishes, it's gone and there is no comeback, no compensation, nothing. Special Delivery is better because it is tracked, but it is equally vulnerable to the organised mail thieving gangs which Royal Mail is full of. In my business we mail a pile of stuff every day and we see this regularly.