The Liberal Democrats have unveiled plans to completely ban gas-guzzling vehicles from the UK's roads by 2040.

Leaders of the party are desperate to improve the nation's air quality and believe many cars, vans and trucks are producing far too many carbon emissions.

The government has set an ambitious target of slashing the country's carbon output by 80 per cent by 2050 - based on 1990 levels - and drastic action will need to be taken if this goal is to be achieved.

A policy document released by the Liberal Democrats said: "By 2040, only ultra-low carbon vehicles will be permitted on UK roads for non-freight purposes."

Although haulage companies will still be able to use HGVs, firms are already coming under pressure to switch to more eco-friendly vehicles.

Some cities have introduced low emissions zones in an attempt to discourage motorists from driving fuel-thirsty cars, vans and trucks into the centre of town, while the government has also made no secret of its desire to see more cargo transported by train, as this will reduce the number of lorries using the nation's roads.