#1, letting it warm up for 10 minutes before driving is part of the problem, not part of the solution. Firstly, it won't warm up much at all just sitting there idling, and second, you are getting ZERO Km per liter, aka infinite liters per 100 Km while it is sitting there idling.
#2, you are no on winter diesel, which is going to increase your liters/100 Km usage by about 10% all by itself.
#3, city usage is hard on the fuel usage. Diesels are best cruising for long distances.
#3b, city usage involves time spent in low gears, sitting at traffic lights, and applying the brakes frequently, all of which waste fuel. Which is why city is hard on fuel usage.
#4, do you make many short trips? Doing so also kills fuel usage because the engine and driveline do not get a chance to heat up properly. During the cold drive, it uses more fuel. Another reason longer drives are better.