How can I slow my thoroughbred down on a hack?? ?

I bought him three months ago, and took him on his first hack with me two weeks ago. He was very hyper and extremely forward going! On the way to the woods, we went on the road, although very hyper he behaved well and felt safe. In the woods and fields he was very hyper and constantly wanting to gallop. Once in canter he would go straight to gallop and barge past horses in front! When holding him back he would fight the bit and try back up from it. Eventually after several gallops, on the way home (on the road!!) he got extremely worked up and wanted to canter home, so i got off him for safety reasons and a more experienced rider got on him, which he then began to buck and rear in the road. Yet in the paddock he is superb! Very well schooled and quite lazy to be honest. What can i do? Does a stronger bit need to be used or a flash, or was it just pure excitement it being all new and all?