Hi Tom,
Listen, take a certain amount of note into what the others have to say by all means, however, what almost all "know it all's" do not undertand is that gross train weight (i.e the caravan and car togther) also comes into the equation, just as much as the max tow weight. Many people only look at the max tow weight of the car, nose ball weight and the maximum weight the caravan can take loaded. Therefore even if you adhere to the above, you can still be breaking the law if the total weight of the car and carvan together are exceeded. I see this subject come up time and time again here and I rarely ever see anyone mentioning the EXTREMELY IMPORTANT aspect of train weight.
However, going back to your situation, I towed my Lunar Stellar with a Fiesta Zetec and the cars kerbweight was 1040kgs the caravan was 1100kgs max and the cars max tow was only 900kgs. However, as the caravan was 870kgs unladen itself I kept all belongings in the car, with habitable items in the van. This then brought it up to 900kgs. The max tow limit has a certain allowence for safety anyway, though I am not condoning this as it could well be invalidating your insurence warrenty etc or breaking the law. The outfit was the most stable I have ever towed. All of this caravan club recommendation, in my opinion is academic as I have had many outfits at 60-75% ratio and they have been inherintly unstable - their are far far more factors which make towing safer than just weight - when will the caravan club start telling people this?
Anyway, I do agree with the others 50kgs over the max tow weight is probably breaking the law and may invalidate your warrenty if the manufacturer demands to know what you tow, although I have never come across this before. I'd also recommend changing your car, but apart from looking at the weight aspect, take into account the stiffness of the suspension (stiffer will generally be better handling for a caravan when towing), rear overhang, profile of tyres etc. I hope I have given you some idea and help. Good luck with your search if you do change the car (and I recommend that you do in this case).
Toby.