Place the haddock fillets with the herbs in a saucepan and cover with milk. Simmer very gently until the fish is just cooked. Lift out the haddock and leave to cool.
Remove the flesh in large flakes and place in a bowl, ensuring there are no bones and skin remaining. Set aside.
Melt the butter in a small frying pan and quickly saute the mushrooms over a medium high heat. Add the lemon juice and season to taste. Once cooked, tip into the haddock bowl. Fold in the chopped eggs and cream. Chill, covered, until needed.
When you are ready to serve return the mixture to a pan and add the prawns. Warm over a low heat, stirring often to ensure the prawns do not overcook and become tough.
Adjust the seasoning and add more lemon juice if needed. Toss in the parsley and serve with plenty of basmati rice.