Charging for road use will come to the fore today when MSPs debate the issue.

Transport Minister Tavish Scott has been forced to scrap a constituency engagement in Shetland to attend the debate.

He has placed the Liberal Democrats at the forefront of the debate, arguing that the UK must move more quickly to find new ways of charging for road use.

After Tony Blair fought back through his own website and the Scottish Tories launched their campaign on-line, Mr Scott will today have to justify the executive's position.

He has previously argued that a road-pricing system would allow the issues of congestion and global warming to be tackled on the basis of an informed decision by electors.

Yesterday his party's Scottish transport spokesman, Mike Rumbles, attacked the Conservatives.

He said: "The Tories change their mind on this issue every week. In the last month alone Annabel Goldie and Murdo Fraser have given entirely differing accounts of their party's position, not to mention the London Tories who have flip-flopped on the subject since the 1980s.

"The Liberal Democrats support a fair system of taxation, coupled with continued investment in public transport, to give people the incentive and choice to leave the car at home when they can," he said.

Tories claimed that a website set up by them committed to opposing further road tolls was so successful that it crashed within two hours.

As a mirror of their London website attacking Tony Blair, the Scots Tory website struck the same political chord.

But Labour responded with quotes from senior Tory figures. "Britain now needs a concerted programme of road building, accompanied by the introduction of advanced traffic management methods, including new solutions for road charging based on usage and the time of day," they said, citing David Cameron.

The SNP dismissed the Tory website as a stunt that added nothing to the debate, pointing out that it had consistently supported the principle of congestion charging in cases where local communities wanted it.