Alright, I'm stumped. (That's what you get when you lend your precious fossil field guides to a forgetful neighbour.) Our Boxing Day walk on Runswick beach turned up a some ammonites, a few bits of belemnites, a piece of jet and a couple of devil's toenails.And this, or rather these since it's obviously a colony of them:
Update; thanks to AndyS and Anon, it turns out they're geological artifacts not fossils. They are cone in cone structures, their origins a matter of debate. While not what I had hoped, finding them caused me (and Number One Field Assistant) some delight, I have learned something and will look at strange shapes in the rocks with a new, skeptical eye in future.
Andy's Fossils. How have I not found this brilliant ammanoblog before? He's a proper collector who cracks open nodules and having found lovely fossils prepares them meticulously then writes about it all very well indeed. Go and see him. At once.