I did mine a year or two ago in Capernwray, a former Quarry and now a dive centre in Lancaster. The water was 4 degrees C and the wind was blowing a hooli. The instructor said at the end of the course it was the only time he'd ever seen waves in there. Because the wind was so strong, we were being blown away from the entrance and water was being sprayed in our faces.
The dive school always get somebody to play 'uncle knob-head' when students are doing the scenarios which adds to the pressure but makes it good fun. I'd echo what others have said about helping out afterwards. The dive school are on a winner with the free assistance but you get an opportunity to keep your own skills sharp. Being uncle knob-head is also great fun!
There was an interesting incident this weekend. I was at the same site with a club member. We were making our way back to the exit, slowly coming up the slope of what was once a road. I spotted a diver, lay prone on the bottom but breathing. I looked at my buddy, who was clearly thinking the same as me. I had a quick glance around for the victim's buddy but nobody was nearby. My buddy was waving his hand in front of his face but he was not responding. I began to manoeuvre myself behind him for a CBL and signaled my intentions to my buddy. Next thing, two divers approached at some speed and we concluded we had stumbled upon a rescue course and left them to it. We surfaced monents later and looked in the direction we had come from to see the rescuers being debriefed by the instructor. The instructor then muttered somthing in our direction along the lines of us interfering, so I congratulated him for the example he was setting to his students by criticising two divers who found an unresponsive diver and followed their training.