Put 3/4 of the chick peas and 3/4 of the flageolet beans in a food processor with the garlic, olive oil (reserving two teaspoons for the relish) and juice and zest of lime. Add half the coriander and season well. Whizz until smooth and creamy, adding a little water if necessary.
To make the relish, toss the remaining chick peas and flageolet beans in a small bowl with the grapefruit segments, olive oil, finely sliced onion and coriander. Season to taste.
Pile the creamy dip into a shallow serving dish or plate and scatter over the grapefruit relish. Grind over plenty of black pepper. Chill until required.