Turn off Seafield Road onto Marine Esplanade, past the sewage plant’s entrance, and you quickly come to the edge of the Firth of Forth. A wide expanse of water with the glittering lights of Kirkcaldy on the other side. There’s a grass walkway here, sandwiched between the treatment works’ chain fence and the sea wall, that leads down to the edge of what then becomes Portobello beach…