Hi Jim,
Assuming the figures you have are not to far out, Based on 1451kg KWt an 85% figure would be 1233Kg, and if you used that figure and the KWt was only 1400kg it only represents a ratio 88% and I would not be overly concerned at that.
Zafiral has made a valid point about the driving licence requirements, but in your case you should be fine as your KWt is 1400 (or may b 1451), and the manufacture a max allowed towed mass is only 1400Kg, the limits of the B only category are not exceeded on either the combined maximum Authorised Mass of 3500Kg, (yours would only be 2851Kg tops) or the MAM of the trailer being more than 100% of the cars KWt.
Lets put some facts to bed though. But a small warning there are lots of different acronyms that may appear to be similar, but they can have different absolute meanings - the sooner an EU wide policy of standardisation of these is made compulsory the better.
85% is not a rule. It never has been, it has always been just a guideline derived four or five decades ago before the towing capabilities of cars were part of the type approval process. All manufactures now publish the maximum braked trailer mass their car can handle. This is a legally sustained figure, and it rarely equates to exactly 85%. Most cars are deemed capable of handling 100% or more but some are actually less than 85% and few are 0% in other word not approved to tow anything.
Whilst I pour scorn on the actual 85% figure, (after all why not 75, 90 or even 100%?) the principal behind it is sound. You should always select the lightest possible trailer (for a given application).
Your Kerb Weight (KWt) is unique to your car. Usually cars are heavier than the published KWt figures, due to manufacturing tolerances, and the some of the manufacture fitted optional items. Check your V5 registration document, this may have your KWt or MIRO figure, or take the car to a certified weighbridge and get a print out - however do make sure you only have the items in the car that are set out for KWt or MIRO measurements.
Towsafe along with most other third party information sites use databases where the information has been entered manually. Consequently they do contain some errors, so you should never rely on them as being accurate. You have no way of knowing which figures are right and those that are wrong. As you point out, Whatcar don't have an exact match for your model, so any result based on 'Whatcar' figure may have no relevance to you. You should always check the figures against the manufacturers own specifications. As the driver you are legally responsible for ensuring the outfit is road legal using the wrong data would be your fault.
You mention but did not post the Maximum Train Weight, this is the ultimate figure that must not be exceeded. With some manufactures the MTW (GTW) may be less than the sum of the trailer allowance and the maximum solo vehicle weight. In these cases you have to trade off some load capacity in the car or trailer to get down to the GTW
Only ever use information form third party sites as a possible indication not as an absolute. That applies to this forum, Towsure, Towsafe, Whatcar and all other similar sites.
Whilst weight ratio does impact on the outfits overall controllability, it is only one of several important factors, others include the way the weight is distributed on the trailer, the mechanical conditions of the car and trailer, and in my view the most significant factor is the driving style which includes speed.
I hope I havn't frightened you.