Cover six eggs with cold water, bring to a boil, simmer for 5 minutes, then chill them in ice water for at least 10 minutes.
Mix the sausage meat, herbs, mace, and mustard well, then divide the mixture into six equal portions.
Peel the cooked eggs, beat the remaining two eggs with a splash of milk, and place the flour and breadcrumbs in separate bowls.
Flatten each sausage portion between lightly floured sheets of plastic wrap until large enough to encase one egg.
Roll each peeled egg in flour, enclose it completely in sausage meat, then coat it in flour, beaten egg, breadcrumbs, beaten egg, and breadcrumbs again.
Heat the vegetable oil to 325°F (170°C), fry the Scotch eggs a few at a time for 7 minutes until crisp and golden, and drain on paper towels.