Bring a large pan of water to the boil and gently lower in 4 of the eggs with a spoon. Cook for 10 mins, then scoop out and rinse under cold water to stop the cooking process.
Peel and chop the boiled eggs into small pieces. Tip into a bowl, then gently fold through the peas, ham hock and mayonnaise. Season. The mayonnaise will help bind everything, but don’t overmix, or the egg will start to break up. Set aside.
Mash the sausagemeat, mustard, parsley, sage and some seasoning together with your hands until well combined. Divide the mixture into 16 walnut-sized balls. Press one of the balls flat in your palm to make a thin disc, then add a heaped teaspoon of the pea and ham filling to the centre. Close your hand to wrap the sausagemeat around the filling, then press and pinch to seal well. Reroll into a neat ball in your hands, then transfer to a plate and chill. Repeat with the remaining sausagemeat balls and filling.
Put the remaining eggs in a shallow bowl and beat, then tip the flour and breadcrumbs onto two separate plates. Season the flour with salt and pepper. Dust the chilled picnic eggs in the seasoned flour, then dip into the beaten egg, then finally roll in the breadcrumbs until well coated.
Fill a large pan or wok no more than a third full with the oil and heat to 180C, or until a cube of bread sizzles when dropped into the oil, and browns in 30 seconds. Lower the picnic eggs into the oil in batches of four or five, and turn every minute for 3-4 mins, until evenly golden and crisp all over. Drain on a plate lined with kitchen paper while you cook the remaining batches. Scatter with some sea salt and serve with mustard mayo or minty tartare sauce, or serve cold.