Madwoman5, statements have never automatically come with ft TA or LSA support, and have always been harder to get for children with autism. Not helpful to make blanket statements like that. A diagnosis is helpful in terms of proving need, but is not a passport to ft 1-1.
Just wanting to make that clear - I've used lots of madwoman usernames and wouldn't want that type of statement attributed to me!
The only thing that will qualify him for additional support is the way his disability affects his ability to access his education. So laying on the floor/ refusing to come inside is all a way in to discussions with the school. If they believe that these types of occasion can be handled with little to no additional support, merely training the staff better in how to spot triggers and react appropriately, then he won't get any additional support. But in that case, it would seem there is no reason for him to miss the trip if there isn't the time or funding to provide additional staff.
I would be wary about sending a child who was unpredictable with routine changes away without additional support, though. It has all sorts of potential to backfire horribly.
Dd2 is travelling internationally with school next month and they are sending an additional staff member. She hasn't had 1-1 support for quite some time (years) but the school recognize that the different environment and change in activities as a direct result of the trip environment, could present problems and have put these measures in place to support her as there is room in the budget to do so. This is a longstanding relationship though, not a new diagnosis where behaviours may have changed recently and caused concern.
Good luck with liaising with the school, op. I'm sure it can be sorted out so that ds and his peers are safeguarded appropriately.