To serve:coriander cress and butter lettuce leaves
Drain butter beans and place in a saucepan with plenty of cold water, bring to the simmer, then cook until beans are very tender (1 hour). Cool in cooking water, then drain, rinse and reserve in cold water until required. Beans will keep refrigerated for 2 days.
Combine scallops, fish, lime juice and chilli and season with salt, then refrigerate to cure (15 minutes).
Meanwhile, cook corn in boiling salted water until tender (1-2 minutes), drain and refresh.
Drain beans and toss in a bowl with olive oil. Serve ceviche and beans scattered with corn, radish, onion and coriander cress and with butter lettuce leaves to the side.