I use to work in recovery with a slide bed lorry with a spectacle on the back So ihave had some towing experiance.
I am quite surprised at how much debate your question has raised, and now I am doubting whether the information you have supplied is in fact the kerbweight for your vehicle, principally because the Kerbweight is not usually on the V5. Its not the same a Mass in Service. or Mass In Running Order. As Lutz has suggested its normally heavier by the weight of the driver which is assumed to be 75Kg and some fluids.
The manufacturer will normally publish kerbweights in the user manual, and even then it's not a precise figure, as it doesn't always include things like teh weight of the towbar, or different entertainment systems fitted in different models.
This is begging to expose just one of the reasons why I find the industry advice to be so inaccurate, and why it can cause so much unnecessary worry for some drivers.
The 85% is only advice, it has no legal or regulatory backing, but whilst I don't find the advice to be particularly accurate, I can't disagree with the underlying principle for the need for trailers to be ket as light weight as possible compared to the weight of the tow vehicle.
I have no idea of what your (not your car's) towing capability is. Whilst you will have some useful addition experiences from your professional driving experience, it has always surprised me how many forum members who have been HGV in some case artic drivers say that pulling a caravan is quite different and is quite different and brings additional challenges to driving.
So please do not assume towing a caravan will be a breeze from the start, be prepared to need to hone some new aspects of driving.
Back to the weight ratio, Without knowing the kerb weight, you cannot actually work out the industry definition of the towing ratio, but based on what you have told us it looks as though its likely to be perfectly acceptable and fairly close to 85% and remember it's not a precise science.
Good luck