The banding system, introduced in 2001, created seven bands of duty to provide operators with greater flexibility to operate vehicles at different weight and axle structures. However, this banding is open to interpretation and the FTA fears operators could be left open to the threat of prosecution.

Sally Thornley, FTA's regional manager, said: 'Previously, articulated vehicles were taxed according to the worst case [ie the least number of axles on the trailer] and the plated weight [or potential of the vehicle combination] was the only weight consideration. The actual operating weight of the combination was irrelevant. If operators wished to take advantage of lower rates of duty by operating at lower weights, they would have to down-plate the vehicle and re-tax it.

'Under the new system, vehicles are taxed according to their revenue weight. For example, a vehicle with a revenue weight of 44tonnes can be taxed in band G or E. If the vehicle is taxed at band E [the cheaper of the two by £650] the vehicle is clearly allowed to draw a three-axle trailer. But within this band the vehicle may also be operated with a two-axle trailer as long as the actual weight of the combination does not exceed 38t and it may also draw a single-axle trailer as long as the operating weight of the combination does not exceed 36t.' If this flexibility is not clearly established legally, the DVLA could be swamped with the administrative burdens of operators up-plating and down-plating vehicles. The FTA is pressing the DVLA to instigate this legislation as a matter of urgency.