The End of Everything by M. John Harrison

Phillip Tennent makes his living at the tideline, collecting artefacts that wash up from the Channel. It's been years since the crisis changed everything, but its exact nature remains obscured. Government barely functions, the seas are full of new creatures, Europe has been mislaid. It feels like the end. Now Phillip has fished out of the water an object he can't keep. A creature that keeps changing. An artefact he must take inland, before it destroys everything he thinks he knows.