Wait, I'm lost. This is obviously a UK school. Was it a public or private school? Were you able to choose allowing your child to go this trip, or not? Could you have chosen to keep your child from going on this trip? Were you given the name of Abernathy Trust prior to the trip? (I'm still having trouble figuring out why people in the UK mix religion with their schools??????)

Sorry, IMO, religions do what religions do. I would expect prayers, Bible reading, and Christian indoctrination to occur because that is what they are and what they do. It's like going to a bar and expecting not to be served alcohol. Did they fully keep all Christian related information about this place from the parents?

Just don't send your kid to religiously affiliated establishments! If this is a public school that required this trip or did not offer a secular option, then that is a bigger problem that needs to addressed. If they misrepresented themselves, in the US, their would be a lawsuit for misrepresentation and other violations.