I think our trailer has got a plated weight of 1450kg... may be mistaken but i am pretty sure it is.
So does that mean that you would add the 1450 to the 1720 of our towing car to make 3170, and that is the overall figure used?? 
If it is the twin axle one I saw you using at oulton park then the plated gross weight will be more than 1450.
Yeah that is the one..
What is the plated gross weight of the trailer? i dont know if it helps but the unladen weight of the trailer is 700kg???
Gross weight is the maximum weight the trailer car be i.e trailer + maximum load, and its the same no matter what is on the trailer. Gross weight is what the police or vosa will use is you get stopped
My three axle trailer is gross weight 3500kg and is stamped on the i.d plate. So basically if you passed test after 1997 and have not done B+E then you can't tow your trailer, empty or loaded.