Well what can i say, coming back from Swansea on Thursday on the mickey 4, i overtook a foreign plated 4x4 pulling a 2x car trailer, i wish i had me dash cam on so i could post a pic, The 4x4 rear axle was well down and on the trailer pulling the cars the first axle tyres was half flat and snaking across lane one, How the hell do they get away with it, would he have been stopped at Dover or Tilbury or whatever port he was going back through, he had 2 cars on trailer prob about 3 and half ton. 
like his one plated at 3500 kg?
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A 4x4 discovery with a towing capacity of 3500 kg would be ok
We run one, can take a surprising amount of weight 2700kg on ours, so 2 smaller modern cars is fine, older stuff is lighter & less of an issue.
will try & post a pic
ok here’s 5500kg train weight on a 6300kg train vehicle. No problems at all, with a 4x4 tow vehicle is important to load the front car on backwards with a centre axle set up or its horrible far too much nose weight & waggy time, the set up as rog pictured are far better in that regard, near impossible to reverse tho!
Ye its was like the trailer, Iquanna put up but this one only 2 trailer axles, so it was snaking real bad and the rear axle on the 4x4 well the leaf springs must of been flat and over weight, the bonnet of the 4x4 was pointing upwards, Good pics though chaps well done.
Loading with insufficient nose-weight is the cause of snaking. Exacerbated by wind, trucks passing, downhill stretches and motorway tramlines. Longer heavier vehicles or vehicles with a short distance from the rear axle to the hitch hide it better but loading is the key. Tri-axles are much more forgiving than singles or tandems with the most stable being the turntable trailer pictured.
I had one for a bit, 23ft bed and 3.5t gross, towed with a Disco.
Carried track cars with it so 800kg each, under 3t all said, train around 5.2t. Positioned the cars for a 75kg nose weight.
B+E, not commercial so all in order, 100% legal as I understand.
Sold it not long after because it was HORRIBLE to tow.
Back massage the whole time over 45mph. Forget overtaking anything.
Piece of cake to reverse though.