The short answer is that although the towing vehicle must be taxed, the towed vehicle does not need tax. This is because the add-on number plate (trailer board) has to have the same number as the towing vehicle. The most satisfactory method of towing a vehicle is to use an "A-frame" such as the type used by AA, RAC, Police, Armed Forces, etc. This can be obtained for around £250 new, or cheaper on e-Bay which is where mine came from. An A-frame or pole would be advisable for the distance you envisage although the A-frame does not need a driver in the towed vehicle (solo towing).
All the best, Peter.
