There are no good dollies, as they are illegal for anything other than recovery, so it's a trailer.
3500 restriction means post 97 like mine, or post 2013 where the rules are slightly different.
Be careful though, as its not simply a 3500kg restriction. For 1997-2013 you need the following:
- MAM (gross weight) of the trailer must be less than the unladen weight of a towing vehicle
- MAM of the towing vehicle and MAM of the trailer must be less than 3500kg
and then implied within this
- You must not exceed the MAM of the towing vehicle
- You must not exceed the manufacturers towing limit
- You must not exceed the net weight of the trailer.
Sadly this means I cant tow a hired trailer with the bora, because the trailer MAM will be 1800-2600kg depending for most twin axle trailers
I also cant tow my trailer behind an empty van, as the MAM of the van puts me over too.
EDIT: Interestingly the rules seem to have vanished from the gov.uk website, so perhaps it's been relaxed...
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/447803/INF30_130715.pdf