Are you talking about putting items such as laptops into the LiPo bag from the beginning to the end of the flight, Peter?
That would make sense to me, but from my experience of LiPo fires, once they're started you're probably not going to be able to get anywhere near the device safely, or pick it up.
If you could, I would have thought that throwing the thing out of the door would be both the easier and safer option, at least if you were over a reasonably rural part of the UK. Over central London or a tinder-dry forest there may be other considerations.