Thanks everyone for the replies

Quote Originally Posted by flamepony12
You might also request to not ride in the dressage saddle? Is there another saddle you may be able to use? If so, I'd try the horse in a saddle that you're sure fits him. If the second saddle you try fits him and he STILL bucks, I'd take a look at his back. It may be sore.
Unfortunately I can't. They seem to have got rid of his general purpose saddle. I don't know what size it was as I never thought of checking. His back doesn't appear to be sore, but next week I'll try applying a little pressure with my hand to different parts of his back to see how he reacts.

Quote Originally Posted by buttercup132
So I changed the saddle and now hes fine. Although he gives tiny bucks cause he's a brat it's not cause his saddle.
LOL! A New Forest mix pony I ride does that, bucking and rearing to attempt to scare me. Silly little guy

Quote Originally Posted by HollandLoppy89
Since I've changed his saddle he's been the best horse I've ever ridden. Try that and see if it helps!
I definitely would if I could. But I couldn't just go out and get him a saddle as he's not mine. The riding school would not accept it.

Quote Originally Posted by Maltese_Love
Maybe the horse is just stressed out?
I've been thinking about that. He's just a cob, so he doesn't have a highly-strung temperament or anything. But there's other things that can worry horses. I'll have to think more on that one.

Quote Originally Posted by Suki Wingy
it really DOES seem like the saddle. Maybe you can present it to someone and ask them to explain why it's NOT the saddle, them they might see that is really is.
That is a good idea. I think next week I'll go for the subtle hint way. For example, I'd take the horse into the arena then say to my instructor:

"Do you know why Dennis has been bucking so much recently? I wonder why, it's not like him at all, is it? I mean, I don't think it's winter fizziness as he's only bucking, so what do you think?" Then my instructor will say something, from which I will suggest that it's the saddle, and then use your idea, Eva. Thanks for that