A friend of mine ;) has just received a speeding ticket for going past a Gatso on the A1 dual carrigeway in Lincs at 71 whilst towing a car trailer.
Apparantly the Gatso can use it's radar to work out the length of the outfit and if it thinks its a car + trailer or caravan or a truck it lowers it's speed threshold.
So be good and if you can't be good do 66!