Firstly, make sure that the crab you have is fresh - unfortunately, this means it needs to be alive.

Choose one which is moving around in a fairly lively manner and ensure that it still shows sign of life right up until you are ready to cook it - crab meat, once dead, deteriorates very quickly and can actually be toxic.

Assuming that 30% of the crab is meat, choose a crab which will yield 100-150g of meat per person - they should also be heavy for their size and smell fresh, not of ammonia.

Prior to cooking the crab, you should put it in a freezer at -18°C for two hours. This is an RSPCA guideline which should ensure that the crab is completely unconscious. Have a large pan full of boiling and very salty water - so salty that a fresh egg floats on the surface - ready, and plunge the crab into this. Bring back to a simmer, and then cook for fifteen minutes for the first 500g of the beast's unprepared weight, and and extra ten minutes for every extra 100g.

You will know when the crab is cooked because the shell will change colour to either dark pink or a reddy brown.