Its just a check to make sure that your car can legally tow your chosen caravan. I think its just a case of inputting your car details, and caravan details onto the towsure website, and it will tell you whether your combination is legal. However, personally I havent had need to do this as the dealers I use do this for you when you buy a caravan, they have also mentioned that it is a legal requirement on their part, but I dont know if thats true or not.
A Towsafe check will I believe cost you £15.95, (for 5) however if you are a member of the C+CC they let you download for free.
Dont know if the CC provide the same service.
Sounds more like a money-making exercise as no-one, not even Towsafe, can relieve you of your responsibility to make sure the outfit is safe and legal. Who can guarantee that they have exactly the correct data that applies to your vehicle? Without seeing it and checking the VIN plate, they can't.
I have to say I used towsure once, a free match at an NEC show for my Honda CRV- Abbey Freestyle, and they gave me totally incorect weights and limits for my Honda CRV, gave me quite a shock, thought I had an illegal match, checked through Honda and with a policeman friend checking VIN numbers etc, all was fine, I wrote to Towsure to complain and guess what, never heard a thing, I just would not trust them now and do all checks myself.