In a large pan of salted boiling water, cook the asparagus for about 3-4 minutes, or until just tender. Half way through the cooking time, add the frozen peas to the pan. Drain (reserving the water to cook the pasta) and refresh the vegetables in cold water, then set aside.
Meanwhile, heat 1 tbsp olive oil in a frying pan over a medium-high heat and fry the bacon for 4-5 minutes, or until golden and crisp. Remove from the pan and set aside.
Bring the salted water back to the boil and cook the tagliatelle according to the packet instructions.
Meanwhile, melt the margarine or butter in a saucepan, then mix in the flour while stirring continuously. Pour a little milk into the mixture and work into a smooth paste. Continue to add small quantities of milk until the smooth paste becomes thick and creamy. Pour in the remaining milk and 60g parmesan cheese, stir well then season to taste with salt and pepper. Stir in the cooked asparagus and peas and heat through.
Once the pasta is cooked, drain and toss with the cheese sauce and the cooked bacon. Mix well and serve immediately, topped with the remaining grated Parmesan.