No Merlin attraction (or any major theme park in the UK) has ever allowed any sort of camera equipment on rides to my knowledge. Although this may seem harsh, you have to remember that not everything is checked by the park. You know that your GoPro chest mount won't break, but the park do not. In the end if you're desperate the theme park has a media and marketing team who are the best people to get in contact with, and if you manage to get explicit permission from the park (this is quite rare) you will be allowed to film.
In regards to kicking people out the park, you have to remember entry to the park is a privilege and not a right, it is privately owned and they can remove you from site for any reason without a refund should the parks rules not be followed by guests.
Just remember to stay safe and respect the parks rules, guys