You can actually tow a trailer over 750kgs even if you passed your test after 1.1.97 but it is complicated!
You can tow a trailer up to 750kgs provided that your Gross train waight (GTW MAM etc) doesn't exceed 4250kgs, so that would mean you could have your van weighing 3500 and trailer weighing 750,
OR
you can tow a trailer exceeding 750 kgs, provided that the train weight doesn't exceed 3500kgs AND that the maximum plated weight of the trailer is LESS than the UNLADEN weight of the drawing vehicle, so in theory you could tow a trailer up to 1700kgs behind a drawing vehicle weighing 1800kgs with a small driver!
As I said it is complicated, and in my view, it was a cock up, because I know of very few people who can advise you correctly on this, (including traffic plods) What they should have said is that you can't tow trailers without a test, then everyone would know where they stand.
I know of one case where a friend of mine who was a 'new' driver bought a caravan which had a plated weight of 1200kgs, and he had a Vauxhall Belmont (remember them???) which had an unladen weight of 1135kgs, and therefore he couldn't tow the caravan with the Belmont as his licence didn't cover him. He bought a Vectra Estate which had an unladen weight of about 1350kgs and he was all legal! Simple Huh!
The best place to look for the information is actually on your driving licence.
The regulations in there entirety can be found here:
http://www.opsi.gov.uk/si/si1996/Uksi_19962824_en_1.htm
with the relevant bit for trailers here:
http://www.opsi.gov.uk/si/si1996/Uksi_1 ... ingpurpose
A worrying part is that if you do want to tow a bigger trailer, the trailer test is the same format as an HGV class one (artic) test, and includes the same manoeuvrability test as an artic, uncoupling and coupling the trailer, gear changing exercise!!! braking exercise, and driving for about and hour! (A bit more involved than the normal car test)
An even more worrying statistic is that only about 70 people have taken the trailer test since the introduction of the regulations in 1997, which means that there are a lot of unlicenced drivers towing trailers, probably without realising it.
The good thing is that not many traffic plods are properly aware of these regs so you woyuld get away with it 9 times out of 10, the bad thing is that insurance companies employ people to negate claims by any means possible. and one of the two factors which invalidate your insurance, (and contrary to popular belief, there are only two) is the clause on your insurance certificate which states "provided the person holds or has held, and is not disqualified from holding a driving licence for this class of vehicle"
By the letter of the law, any driver who passed their test since 1997 simply does not hold a licence authorising them to drive vehicles with trailers exceeding the limits outlined above, so therefore they aren't insured.
So if you tow a trailer and you haven't got the relevant licence, you aren't insured, simple as that.
and still got a clean licence 
