1. If using fresh octopus, beat it with a meat hammer to tenderise, then rinse well under cold running water, using a clean sponge, to remove any excess saltiness. If frozen, you don't need to do this, as freezing has the effect of tenderising it.

2. Bring a large saucepan of water to the boil (but do not salt it, as this will toughen the octopus), add the octopus. Cover with a lid, reduce heat to low, simmer gently for 20-30 minutes, or until tender. Drain well and cut into bite-size pieces.

3. Meanwhile, bring another saucepan of water to the boil. Add the squid bodies and tentacles. Simmer over a low heat for 10 minutes, remove with a slotted spoon and set aside. Add the prawns to the same water, simmer for 2 minutes, or until they have changed colour and are just cooked. Remove, then peel 3/4 of the prawns, reserving a handful for garnish. Cut squid bodies into strips. Set aside.

4. Place the mussels and/or clams and white wine in a large pan over a high heat. Cover and cook, shaking the pan occasionally, until the shells have opened. Remove from the heat, strain, reserving the cooking liquid. Discard any that haven't opened, remove the meat from the rest and discard the shells.

5. Place the prawns, octopus, squid, mussels/clams and celery in a shallow serving dish. Whisk 50ml of the reserved and strained cooking liquid from the mussels with enough lemon oil to taste. Drizzle dressing over the seafood, season to taste. Scatter with the parsley and garlic. Serve immediately.