To cook the octopus tentacles, place them in a large pan of water with the red wine vinegar. Bring to the boil and simmer for 40—60 minutes, or until tender. Cut into slices.
Cook the potatoes in boiling salted water and drain. Leaving some whole and halving others, put them into a bowl with the fennel and olives. Drizzle with the extra virgin olive oil, lemon juice and white wine vineg