I was playing around with saddle angles today on the Pashley. Over this past week it was starting to feel like I was sliding off the back of the saddle and so I was nosing it down a little. In my enthusiasm, I apparently favored one nut when tightening, pulling the bolt through the clamp and causing it to round out the square hole that it goes through. You can see that the bolt has flat spaces at that fit into the square holes. This keeps the bolt from turning around in the clamp, and when one gets pulled through, neither flat is in a hole.
So, while trying to back this mistake out, I got both nuts cross threaded on the bolt since it wasn't staying still in the clamp! Go me! And boy did I get the nuts cross threaded on there good. So my most wonderful husband, whom I now owe a chocolate malt, came to my rescue and sawed the bolt in half, by hand! This was the only way we could free my saddle from the clamp.
So, lesson learned. With the Brooks type clamps, don't tighten from just one side. Keep the bolt even.