Croqueteer
I don't see much difference between 'safety pilot endorsement' on a PPL and a NPPL. The letter of the law and clear intention is that the pilot CANNOT fly solo, nothing more. He [the CAA] did indicate a Class 1 scenario would be a completely different kettle of fish.
Give them a call for your own peace of mind. He was relatively friendly and concurred that the chances of two private pilots keeling over simultaneously was pretty slim.