Fortunately, I have found a nice little fertiliser which gave them a new lease of life, and best of all, I made it at home with recycled food scraps from the kitchen.
I put a banana skin, three eggs shells and the coffee grounds from my morning coffee in the blender and turned it into a paste (thinned with a little water), then spooned it into the plants and watered it in (I used 1 tsp of fertiliser per plant). They sparked up again well and are now sprouting new growth.
It was excellent plant first aid and alleviated my feelings of guilt about neglecting them so appallingly. It seems to have worked on cyclamens, orchids, ferns and potted herbs.