Shell and devein shrimp.
Place shells in a pan with 2 1/2 cups cold water, cover, bring slowly to the boil and simmer for 15 minutes.
Strain off fish stock.
Dice shrimp.
Remove rind from salt pork and dice, (cut bacon into 1/2 inch strips).
Fry salt pork in oil in a large heavy pan until golden brown, remove from pan.
Gently saute chopped onion in fat remaining in pan until soft and transparent.
Scrub new potatoes and slice thinly.
Add potatoes and tomatoes to pan and saute for 1-2 minutes.
Add fish stock, cover and simmer for 30 minutes, or until potatoes are tender.
Add shrimp and milk, heat through gently and add salt and pepper to taste.
Stir cream in just before serving, if used.