Put the beans into a bowl, cover with plenty of cold water and leave to soak overnight. Drain the soaked beans and put them into a saucepan; cover with cold water.

Bring the beans to the boil, then lower the heat and simmer over very gentle heat for 3 hours until tender, topping up with more water if necessary. Transfer to a colander and drain thoroughly.

Heat the oil in a frying-pan and gently fry the onion and carrot for 5 minutes, until the onion is soft and lightly coloured. Add the green pepper and fry for a further 5 minutes, until the vegetables are just tender.

Add the beans, tomato puree and herbs to the pan, mashing the beans with a spoon to make the mixture hold together. Season with salt and pepper to taste.

Divide the mixture into 8 and shape each piece into a neat, flat circle. Beat egg and water together in a shallow bowl and spread the breadcrumbs out on a plate. Dip the burgers first into the beaten egg mixture, then into the dried breadcrumbs, making sure they are well coated.

Heat the vegetable oil in a large frying-pan, add 4 burgers and fry over moderately high heat for 3 minutes on each side until crisp and browned. Remove with a slotted spoon, place on a serving platter, and keep warm. Fry the remaining burgers in the same way and serve at once.