Depends on the year, model and transmission etc. The easiest thing to do is check the weight plate on the car, subtract the gross vehicle weight from the gross train weight and you will be left with the max trailer weight you can tow. Citroen often quote a max towing weight with only the driver in the car and the weight of any passengers or luggage then has to be deducted from the possible trailer weight hence getting lots of different figures. If the outfit is checked by the Police etc they will go by the plated weight on the vehicle so that is the safest figure to use.
Read through the handbook. Somewhere in there should be max braked tow weight. You won't want to be towing much more than a tonne with a 1.6 diesel for reasonable towing performance though.
You need to know the gross train weight from the weight plate on the car. Deduct the gross vehicle weight (2250) from the gross train weight and you will get the max trailer weight. The figure of 1180 you have given above says with weight transfer so I expect if you deduct 1180 from the gross train weight you will end up with a figure lower than 2250. This means that the max trailer weight will be less than 1180 if the car is fully loaded.
Come back to us with the weights from the weight plate and we can work it out for you.