Heat a little oil in a large heavy frying pan over medium heat. Cook the sausages, turning occasionally, for 15–18 minutes until deeply golden all over and cooked through.
Add the bacon rashers and cook for 2–3 minutes per side until crispy. Keep warm.
Cook the mushrooms in butter with a little salt until golden. Keep warm.
Place the tomatoes cut-side down in the same pan and cook for 3–4 minutes until softened and slightly caramelised.
Fry the black pudding slices for 2 minutes per side (if using).
Fry the egg in butter to your preference — sunny side up, over easy, or basted.
Toast the bread. Arrange everything on a warm plate: sausages, bacon, egg, mushrooms, tomatoes, black pudding, baked beans and toast. Season and serve immediately.