@iwasjustwonderingreally There two separate questions here. No, teachers should not be getting drunk while in charge of children. They ARE allowed a couple of drinks in the evening but one or two staff should avoid drinking in case of emergency. When I run a trip we take it in turns, but if I am in overall charge I generally don't drink, or I have one beer with dinner.
However, whether or not the parents pay for the teachers to go is irrelevant to any safeguarding complaint. As it happens, the educational visit company will allow one free place for a teacher per X students, so no the teachers don't pay, and I suppose the students are paying indirectly in the price they pay.
However, having run residentials abroad (not skiing), I can tell you it takes a minimum of 50 hours of unpaid admin to get a trip going. Chasing parents for passports, EHIC cards, writing risk assessments, corresponding with tour company, writing letters to parents, dealing with stupid questions about why they need a passport (?!), working out rooming arrangements and checking with all Heads of Year that you haven't inadvertently brewed disaster etc. Then you get on the trip and discover someone has an undisclosed eating disorder, you have parents phoning you because a child doesn't like the way her bed faces, kids fall out with each other and phone mum in the middle of the night and she phones you, another child asks what is the best way to kill yourself, another child (who you didn't want to take because of his behaviour but were told it was discriminatory not to) climbs out of his dormitory window (ground floor thank God) at night and somehow breaks his ankle, and you and the other teacher on stay sober duty spend all night until 4am at the French A&E with him and then have to stay awake through the following day's activities, then you have sweet and lovely but clearly very precious year 7's coming to your door at midnight in tears because they are homesick, because their parents have never even attempted a sleepover before and yet somehow thought several nights abroad was going to work because they fancied a break themselves.... The list goes on. And the constant worry that someone with a nut or wasp sting allergy has mislaid their epipen and so you are yourself carrying 4 of them around permanently. And then you get back late at night and ALL you want to do is go home and sleep, but several parents are two hours late picking up because they misread the letter and weren't answering their phones. And they don't even say thank you for taking them, or thank you for waiting with them.
And on top of all of this, because you kindly travelled at a weekend and on your day off, those days are completely unpaid.
So yes OP, feel free to complain about the teachers who drank on your child's residential. I wouldn't be too happy with this either. But before you do, bear in mind how hard it is for schools to find teachers who are willing to give up their weekends and half terms unpaid for this level of stress. If you want your DC to even HAVE school trips to go on in future, tread carefully.