In a large saucepan sauté the onion, carrot, red pepper, marrow and garlic in a drizzle of olive oil. Sauté until the vegetables are soft. Season.
Remove from the pan and purée the vegetables using a hand blender or food processor. Set Aside.
Using a food processor, pulse the mushrooms until they are very finely chopped. In the same pan used to cook the vegetables, sauté the mushrooms in a drizzle of olive oil until they have sweated off most of their water, about 10 to 15 min. Set aside.
Again in the same pan brown the mince in two batches using a little olive oil per batch. Lightly sprinkle the flour and worcestershire sauce over the mince while it is cooking.
Once both batches are browned add the mushrooms and blended veggies back to the pan along with the tin of tomatoes. Bring to a simmer and cook for 30-40 minutes until the sauce has thickened.