David
we have a Sport 4-Motion 140 bhp TDI estate manual(weighed 1640kg on weighbridge with no driver, 90% fuel and no extra kit in car), pulling a Bailey Senator Indiana (MIRO 1248kg, MTPLM 1500kg) loaded to about 1450kg. We get 25-27mpg towing, 47-52mpg Solo (this is with DPF, which reduces mpg over std engine). We got this model as the 4-Motion is some 100kg heavier than the 140 estate with DSG, which we took on a test drive to the same local weighbridge (it weighed 1530kg). Its powerful enough, maintains 60mph in 6th (mostly), but doesn't attack hills like our old X-Trail 2.2 diesel 136 bhp.
Mind the weights stated in VW brochures - they are not reliable.
Of the 2 cars, fuel consumption is similar towing, but solo, the Passat wins.