Heat the oil and butter in a heavy based frying pan, pan fry the beef fillet for 2 minutes each side - they should be rare in the middle - cook for longer if you prefer. Transfer to a plate.
Fry the pancetta and porcini mushrooms in the juices in the pan for 5 minutes until slightly golden.
Add the red wine, leave to bubble for a minute, then add the Tracklements Cumberland Sauce, heat through for a couple of minutes.
Serve the beef fillet with a little sauce drizzled over the top, eat with creamy mash and steamed green vegetables or salad.