Wash and finely chop the spring onions.
Crush the crab meat with a fork, removing any pieces of shell. Mix the crumbs with the crab meat.
Place the egg and mayonnaise in a bowl. Mix with the mustard. Add the parsley and Worcestershire sauce. Stir well until smooth.
Fold the spring onions into the crab meat and mix with a spatula. The mixture should be a good shapeable consistency. If it is too soft, add some breadcrumbs.
Using damp hands, remove 3 tbsp of the crabmeat and form into a little cake. Continue making the crab cakes until all the mixture is used up.
Heat the butter and oil in a non-stick pan. Add the crab cakes and fry gently for 3-4 minutes until golden brown.
Turn with a spatula. If necessary, add more butter to the pan and fry the other side for another 3-4 minutes.
Lift the cakes from the pan with the spatula. Drain on a plate lined with kitchen paper. Serve with lemon slices.