Heat the oil in a medium saucepan. Add the onion, gammon and leeks and cook for four minutes.
Add the peas and stock to the saucepan and cook for 3-4 minutes.
Transfer the mixture into the bowl of a food processor and season with salt and freshly ground black pepper. Blend the mixture until the soup has a smooth texture. Pour the soup back into a saucepan and simmer until hot all the way through, but not boiling.
To serve, pour the soup into a clean bowl and garnish with the double cream.