Technically, this wasn't your simple pickled herring. I shopped in Sainsbury's for this and they had either rollmops or marinated herring. For information a rollmop is pickled herring, wrapped around pickled onion, in pickle/vinegar. The marinade though is a sweet dill marinade, consisting of a basic pickle with the addition of some spices and dill, of course. So it's better than just pickled herring right? Wrong. At least not on toast avec un oeuf.
The herring packed a mighty kick making your eyes water. Boiled egg on toast is good, but not known for its strong flavours and the herring just destroyed everything in this slice. Grace couldn't even finish. Not that that's a first!