Add the chicken to saucepan of water and bring to the boil, then simmer until tender.
Blanch the leeks.
When the chicken is cooked drain the water and transfer to a pie dish. Drain the leeks in the same way and add to the chicken, mix in the ham and season well.
In a large saucepan melt the butter, then stir in the flour to make a roux.
Gradually stir in the milk when you have added all the milk, worcestershire sauce and mustard, bring to the boil and simmer for 2 minutes, until thick and creamy.
Pour the sauce over the chicken, leeks and ham and stir together well.
Roll out the pastry and cover the chicken, leeks and ham. Brush the top with a little beaten egg.
Cook for 25-30 minutes at 175C.
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