The continued uncertainty over the safety of public transport is causing more people in Britain to drive after the novel coronavirus-caused lockdown, prompting a warning that air pollution could become worse than normal and scrutiny of the government's green roads policy to encourage cycling and walking.

The warnings come in the lead-up to "Week 38" next month, when the number of hospital admissions of children suffering asthma reaches a peak just as schools reopen.

The Transport Secretary Grant Shapps has pushed through a 250-million-pound ($327 million) program to promote a "new era for cycling and walking", but complaints have been raised by campaigners who argue it only increases pollution and that new one-way systems and road closures merely shift traffic congestion elsewhere.

Last week, road traffic in the United Kingdom exceeded pre-lockdown levels for the first time, The Times newspaper reported.

Rosamund Kissi-Debrah, whose daughter Ella died from a rare form of asthma thought to have been exacerbated by pollution near her South London home, said: "I'm not against green traffic measures or low traffic neighborhoods, but where I live in Lewisham it has become a nightmare.

"Unless something is done, it is going to get worse when schools reopen and more people return to work," she told The Telegraph newspaper.

Kissi-Debrah, now a World Health Organization, or WHO, advocate for health and air quality, said she fears new road closures in the run-up to Week 38 could create the "perfect storm" and increase child asthma cases, putting further pressure on the National Health Service.

Asthma UK and the British Lung Foundation, which merged in January, warned that road traffic could rise far higher next month when schools return and people start going back to workplaces.

The charity said that uncertainty over the safety of public transport would lead to people choosing to drive instead of taking the train or bus, causing air pollution to soar.

It is urging the government to use the upcoming Environment Bill to set a strong new legal target, based on WHO guidelines, for fine particles, the most dangerous form of air pollution.

In the first few weeks of lockdown, road traffic fell to as low as 23 percent of normal levels and there was a sharp reduction in air pollution, particularly nitrogen dioxide, which is largely produced by diesel engines.

Cycling tripled on some days in the early weeks of lockdown, and is now about 50 percent higher on some weekdays and is still almost double the normal level at weekends.

Jonathan Grigg, professor of paediatric respiratory and environmental medicine at Queen Mary University of London, said that the rise in traffic was "really disappointing — this means that people who have taken up cycling during the lockdown are going to be exposed to pre-lockdown levels of traffic-related air pollution.

"We are missing a unique opportunity to remove the most polluting cars and vans from our roads. There should be a 'scrap diesels to help breathing' scheme."