HELLO Pip
My sources show two models of Diesle estate, and sadly nither is rated to tow your caravan.
Focus 1.8 Diesel esate (built up to 2002)
Model Kb wt Max permitted Tow Mass(Kg)
1.8 90PS 1295 1200
1.8 115PS 1317 1300
The manufcatures stated Maximu permitted towed mass is an absolut legal limit, and you must not excede it.
Please check with your Ford Dealer for confirmation, but if these figures are correct you cannot legally tow 1313Kg with either model.