Graham
If you havn't got an owners manual with the van, has the caravan got a plate or sticker anywhere. Usually around the bottom of the door or on the A frame at the front. If not it may be worth contacting Swift Leisure to see if they can help.
The same applies to the car. The weight information should be in the owners manual. Sometimes there's a sticker on the pillar inside the drivers door. If not, try www.whattowcar.com and see if your car is listed. If this doesnt help, post more details of your car model, year, engine etc) and I'll try and help.
Marcus