Scotland would have entirely free public transport under plans being put forward at the Holyrood election by the Scottish Socialist Party.

The far-left group, which has four MSPs, reckons the bill would be less than £1bn per year to pay the fares for everyone using rail, bus and ferries in Scotland, including the increased demand for travel that would result from the removal of fares.

They also believe savings elsewhere could cover the cost of nationalising all public services, including railways, Stagecoach and First Bus.

The audacious, eye-catching idea is set to play a central part in the party's campaign, with a pitch to make Scotland the first in the world to make public transport free, taking a lead in reduction of climate-change pollution.

Its reckoning is the cost would be partly covered by the reduced cost of accidents in private cars and of lower road-maintenance costs, together coming to "anything between £300m and £500m". The economy would be boosted by people spending their bus and train fares on other goods and services, helping a million workers each re-direct between £40 and £100 per month.

Businesses could be saved as much as £1bn per year from reduced road congestion, the party claims. Tourism would be boosted and there would be lower demands for oil imports.

According to one leading transport expert, it would require a doubling of the number of people travelling by rail to reduce vehicle miles on the roads by as little as 5%.