Clean air zones (CAZs) are a central pillar of the Government's response to air pollution. Although charging CAZs, where drivers of certain classes of vehicle are charged for entering the zone, have not been universally popular, they have the potential to have a substantial impact on air quality. London's ultra-low emission zone which follows a similar approach has reportedly led to a 37% drop in NO2 concentrations within the central zone.

Charging CAZs are now planned in many cities across the UK but so far none of them have come into force and the implementation of some has been paused due to the COVID-19 pandemic.

In some cases, these delays are due to the anticipated profound impact of COVID-19 on the economy. In others, where plans were less advanced prior to lockdown, delays have resulted from local authorities' attention naturally being focused on the immediate crisis and the difficulty of conducting meaningful public engagement with restrictions on movement in place.

So far these delays have had little impact on air quality. Lockdown has led to a dramatic drop in air pollution, and it is hoped that as social distancing reduces capacity on public transport, we will turn to walking and cycling rather than private cars. This could translate into a re-consideration of the need for, or scope of, CAZ proposals.

However, the current improvement in air quality could be quickly reversed. Initial enthusiasm for walking and cycling may wane as winter months set in and private car use could increase. A sustained recession could also delay the switch to electric vehicles by both individuals and businesses who may put off expensive fleet upgrades.

Initial data appear to suggest that a shift towards private cars may already be happening. Car use dropped to around a third of normal levels at the start of lockdown but it was back up to 65% by 1 June. In contrast, National Rail use was still only at 6%, London Underground at 10%, and bus journeys nationwide at 17% of pre-lockdown levels.

If these trends continue, the need for CAZs could become more pressing than ever. So where does this leave local authorities' CAZ plans?

For authorities with CAZs in the pipeline there is likely to be increasing pressure from campaigners to implement them. The health impacts of air pollution, including a potential link with COVID-19, are more widely accepted than ever and having experienced the benefits of cleaner air over the last few months, many will not want return to breathing dirty air.

However, these authorities may need to consider whether their current plans remain appropriate. For example, if we do see a significant decline in the use of public transport, clean air plans may need to be adjusted to address the impact of increased private car usage.

For authorities who may be considering whether a CAZ or low emission zone could be introduced in their area, this may be the ideal opportunity to move plans forward. As we explore new ways of living and working in response to the pandemic, there has perhaps never been a better time to consider more radical schemes and policies.

Of course, CAZs are not the only option available. The Transport Act 2000, which permits the road user charging schemes used to implement CAZs, also introduced the ability for authorities to set up workplace parking levy (WPL) schemes. Instead of charging individual drivers, WPL schemes impose a charge on employers who provide workplace parking. The aim is to encourage carpooling and use of alternative modes of transport while raising much-needed revenue for other transport improvements.

Only one WPL scheme has been introduced so far but the results have been promising. As well as tackling congestion, Nottingham City Council's scheme raises around £9m a year to fund public transport improvements.

As movement restrictions ease and travel increases, local authorities have an opportunity to facilitate a shift away from more polluting forms of transport and drive a long-term improvement in air quality. CAZ and WPL schemes, when coupled with improvements in active transport infrastructure and incentives for low-emission vehicles, have the potential to play a key role in this transition.

Laura Thornton is legal director and Andrew Lister is associate at BDB Pitmans