The turtle wont make it 8 hours without water--you are not going to be able to shove it in your pocket or duffle bag.
The only way you could take your turtle to England with you would be to put him in a tupperware-type container with a lid on your lap on the plane. If you get a container something like you would use in the refrigerator to store iced tea or KoolAid in that has a flip-open spout, the container can stay closed while you board and debark and you can flip open the spout to provide fresh air while you sit still while allowing for little spillage. I dont think you could hid such a thing though. You will have to openly ask permission to carry the turtle with you.
Beside that, think of what would happen if you got caught sneaking the turtle in at the airport? They would probably take him form you and you would be forced onto the plane with your parents without him. Nobody would care for it and he will end up getting flushed down the nearest toilet or just left to die somewhere. Some doofus might be kind-hearted enough to put him outside for a chance at survival after their shift at the airport, but doubtful. (Sorry I am assuming you are a kid just by the question).
I know that they take things from you at airports. I had a lighter once and I had to fork it over and also had a large decorative pin that was taken once (could be used as a weapon). You dont get these things back--they are just gone. If you dont want your turtle gone, you are going to have to make legal arrangements or you will run the chance of having the turtle taken at the airport.
If worse comes to worse, you may have to look for a friend to give the turtle to before you move if you cant take him on the plane in the tupperware (hopefully the turtle is small). I think they might let you do it if you keep the container on your lap. Think about the turtle's safety and do the right thing by him. Give him to a friend or take him with you legally.
Life as I lived it