DJM, you quoted the police as saying "We knew before this stunt took place that there was no risk of serious injury to anybody and we discussed this with Channel Four in some detail before it took place". Contrary to your claim, the quote doesn't mention permission at all, let alone permission to use a real pistol. It implies the police had been told why the stunt involved no risk of serious injury. They would have been told that Derren would not use a real pistol or real ammunition, making the conclusion inevitable.
Edit: I've just read Azrael 5's post above, which confirms Derren would have needed a licence not just for a real pistol, but even for an airgun. The gun laws are such that he couldn't have got a licence for a real pistol even if he'd wanted to.
Are you saying that Penn and Teller have performed with real pistols in the UK since the UK law was tightened up? If so, why would Derren go to Jersey? In my opinion, he went to Jersey in order to get more publicity. He wasn't just picking somewhere with less strict gun laws, since, as I've said, he couldn't have got permission for a real pistol in Jersey any more than he could have got it on the UK mainland. If he'd obtained a permit, he could have got even more publicity by showing it to the press, but he hadn't and therefore couldn't do that.
If you recall, DJM, volatile posted "He does NOT use professional actors", with no exceptions mentioned. There was no disclaimer about use of actors in Derren's introduction to the Trick or Treat show I mentioned, and Derren stated in the show that all the people (shown in the background in part of the show) were actors. They could have been described as assistants or other volunteers, but they weren't. Despite their minor role, they were all stated to be actors. If anything, it was the departure of the actors that made things more dramatic (by leaving the subject alone), so almost any bunch of people could have been used. I'm not objecting to that use of actors, just pointing out that Derren sometimes says he has used actors as well as sometimes stating that he has not. On another occasion, Derren used Robbie Williams and needed him to play along, i.e., act as a stooge, which Robbie did, although not particularly well - he seemed almost pleased to see "blood" dripping from his arm!
I've now seen Trick Of The Mind, which was repeated by Channel 4 in the UK on 17th July, so I've watched Helen behaving a bit oddly with a stone. Helen seemed to want to keep away from the box, rather than having fear of the stone. Perhaps the box contained something frightening, such as a snake or large spider.