Need some advice whilst buying a car (for towing?)

Correct me if I’m mistaken, but isn’t the 85% rule (recommended): the caravan should not weigh more than 85% of the car’s kerb weight.

That is the recommendation, ATB, and is probably what the other poster meant. That is, the car’s kerb weight is heavier than the cvan’s all up weight in a ratio of around 100/85.  

You've lost me there, surely you mean subtract the MTPLM of the caravan from 3500kg which will give the weight of vehicle you have to play with. Subtracting the MTPLM of the caravan from the maximum weight of the vehicle will leave you with next to nothing.

Correct===That's what I meant to say. cheers.

Do all road users and you a favour and pass the B+E test. Mucking about with weights, you could very well end up being unlicensed. Don't forget thet every car is different, and every accessory adds weight to that car, even the tow bar, and they are very heavy. If you go over that 3500kg limit, you will be unlicensed. Plus trying to find a car that will legally tow it may be much costlier than doing the test if it struggles to pull it. Maybe fit a motormover for the four miles?

Two weeks a year and it is stored four miles from the site? What is the point? Do your test and venture out into the World. Each to their own and all that, but the same place every year and you don't even tow it there yourself? Sorry, but my dog has a more exciting life.