The move comes on the first day that London motorists face charges to drive into their city.

MSPs including Tory transport spokesman David Mundell have addressed a conference on traffic congestion in the Scottish capital.

The one-day meeting, organised by the Scottish Transport Studies Group, debated attitudes to congestion in Scotland.

David McLetchie: Fighting the charge

Motorists travelling into central London have to pay �5 after the capital's congestion charging scheme came into force on Monday morning.

London Mayor Ken Livingstone warned that the first few days of the scheme were likely to be chaotic.

But a smooth start to the new charging regime was reported.

The charge is aimed at cutting congestion and raising much needed funds for public transport.

'Unfair tax'

A similar scheme could be introduced in Edinburgh by 2006, depending on the result of a city-wide referendum.

But the Scottish Conservatives are totally opposed to the move.

Scots Tory leader David McLetchie said congestion charging was "nothing more than an additional tax on motorists".

He added: "Road tolls will bring no benefits to any of the cities in which it is introduced - it will only serve to punish certain groups of people.

"Businesses in Scotland already pay higher rates than the rest of the UK and city entry charges will simply put business in Edinburgh at an even greater competitive disadvantage."

The Tories want to make road user charging a key election issue in the Lothians

Road tolls will bring no benefits to any of the cities in which it is introduced - it will only serve to punish certain groups of people David McLetchie Scottish Tory leader

Stephen Howell of Transport Initiative Edinburgh, the body in charge of introducing the scheme, said it was "necessary" to maintain the economic vibrancy of the city.

He said: "We believe that with Edinburgh growing as fast as it is, the city's traffic will slow down even further.

"We wish to ensure congestion-free streets for a prosperous Edinburgh."

Neil Greig of the AA said Scottish road users already paid the highest charges in Europe.

He said: "Scottish drivers are quite happy with the current system of paying through the fuel pump.

"They just want that reformed so that more of the money they pay goes back into transport improvements they can see and they can use."