The warning is given in a letter to Department of Transport officials by the Government's landscape watchdog.
Roger Clarke, the Commission's Director of Policy, is seeking the publication of further research on this matter. But evidence so far suggests that even at a low charge of 1.5 pence per mile for cars and 4.5 pence per mile for lorries, there could be a 10 per cent flow diversion.
Responding to the Green Paper, Paying for Better Motorways (Cm 2200), the Commission says it is not opposed to the principle of charging, but feels any levy should fit within a wider national strategy for traffic demand management, recognising that road space cannot grow at the same pace as travel demand.
As 85 per cent of all traffic is non-motorway, congestion and environmental costs are already higher for ordinary roads than for motorways., said the Commission.
Severe landscape damage will also result from 100 miles of new motorway envisaged in the present roads programme, together with a further 500 miles of widening to existing motorways. In addition, more new motorways bought by private funding, could further increase damage to unspoilt countryside.
New motorways are arguably undermining local economic activity by encouraging long distance commuting, resulting in environmental loss for no economic gain, says Dr. Clarke.
In the long run, if travel needs rather than freedom and mobility for road users is the main consideration, the use of fuel taxes and vehicle excise duty could well be part of a more effective overall approach to traffic management, says the Commission.