My housemate and I were stuck in Bullpot farm with a very large, very dodgy and semi-falling apart van. The track back down to the valley bottom was covered with a lot of black ice / water ice. We couldn't leave first thing because wanted to see if the sun would thaw it a bit, which meant that we had to go caving again to pass the time. Such a shame.
Eventually made it down but the drive was absolutely terrifying!