[loki]

London? It's not fancy fertilizer or anything like that, it's your climate. Eggplants need it hot. Warmer than tomatoes by about 5 degrees. London is not hot. I am in a short-season area, with warm to very hot days and cool nights. I use black plastic mulch (actually it's dark green now), and row covers (a moderate agrofabric that adds about 5-8 degreed F protection). I leave the row covers on till it's about 60 at night (end of June - early July usually). The combination warms up the soil early, and keeps the heat in at night. The plants are three times larger compared to not doing this! This might help you but I'm not sure even that will warm it up enough? Other than that, eggplants are easy. They do need fertilizer but nothing very different than tomatoes. They can tolerate more nitrogen since they don't stop producing fruits like tomatoes do with higher levels of N (at least for me). One other thing, but it does not sound like it's a problem for you: eggplants are not resistant to various fungal diseases that the solanaceous plants can get, whereas tomatoes and peppers do have resistant strains widely available. But these diseases are readily apparent.