Towing on a motorway is not prohibited. However, what many do not understand or indeed comply with is that there are many rules to how towing can be legally carried out.
For example you cannot use a rope that is too long or too short. You must display an 'on tow' sign to the rear and you must display the registration mark of the towing vehicle on the rear of the towed vehicle. Obligatory lights of the towing vehicle must be displayed and effective at the rear of the towed vehicle.
Just putting a tiny hand written on tow sign in your rear window and using hazard lights is simply not safe, enough or legal.