Ballast when towing?

Yeah well... Fair point  . The fact that the driver is aware of the extra stopping distance is the main thing. 

In my opinion, the tow capacity of any vehicle is not determined by whatever number is on the plate/manual/towbar (within reason of course)

It's entirely up to the chap behind the wheel. If the driver can't operate and load a trailer correctly, the official tow rating won't matter a hoot. Most accidents i see over here involving trailers are caused by poor loading / weight balance or simply untrained drivers - underestimating stopping distance etc. as above.
I'm not suggesting for a minute anyone here hasn't got the nous to tow a trailer, it's just my general observation. A little common sense and a practical outlook goes a long way. 

Edit: sorry, I'm replying to rogers reply to my previous commment. Forgot to quote. 

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So has anyone towed a caravan with a Gen 4 Jimny, as in something around 1,000kg rather than lightweight camping trailers and very small/light caravans?

We've got a Swift Basecamp 2 which is 1,000kg. l've not yet tried to tow it with the Jimny.

ln the tow car awards the Gen 4 Jimny was awarded 1/5 "very poor" and on test they used the same caravan as ours.

I assume they're comparing it with larger SUV's (like our Defender) and it obviously won't do as well as those, but will it actually do it safely and without holding everything up on hills?

I've towed a caravan with all the vehicles I have owned, my G3 Jimny included (caravan and Jimny in my profile picture). It's towing about 750kg braked. I admit it's not a G4 and 1000kg as requested, but expect the experience to be about the same for the G4 with the extra 250kg negating the extra 200cc.
Stability isn't the issue, the Jimny from this respect tows very well. The caravan has little effect on the vehicle, it steers and stops almost as if it isn't fitted, one of the better tow vehicles from this respect.
The lack of engine power is the major issue, it just doesn't have enough to make it a pleasant experience. Yes it can do it and so long as you don't mind using the gearbox it will keep moving forward, but it can get a little scary. You will see 30 mph on motorway inclines, I got around this by travelling at night whilst the impatient world slept.
I would hope the G4 is better due to the extra 16 bhp, but I suspect it still not enough especially if you want to tow more at 1000kg.
Don't fear the experience, it will do it just fine, but it's not going to be fast and expect to rev the hell out of it for sustained periods.

Towing also moves the maintenance schedule to "severe use", so transmission and engine fluids need changing on a more frequent basis.  Change mine yearly, the rear axle gets particularly hot for some reason, but it never caused issues.
 

The issue with caravans isn't the weight so much as the size. The Basecamp 2 is about 60cm wider and 80cm taller than a Jimny. That's a lot more air to displace! It's also 5.1m long which gives it a lot of rotational inertia for a short, lightweight Jimny to resist.

By comparison, the 1,300kg load of my firewood trailer is no wider or taller than the tow car and roughly the same length. I have similar power to a Gen4 and can maintain 60mph up a reasonable incline in 4th gear, but I'm sure with the extra drag of a caravan this would reduce dramatically. Add a head wind and it would probably half it.

The Jimny is a great small tow car but it's not a great caravan tow car.