Air pollution in Britain is a pervasive killer, but it is also intangible and invisible. You can rarely see it, you can't always smell it, and it is unlikely you will ever hear it. It is even less likely, apparently, that you will have heard about it if you happen to be a Conservative Party minister.
Environment Minister, Therese Coffey, and Minister for Exiting the European, Robin Walker, were recently subjected to scrutiny from the Common's Environmental Audit Committee where they faced questioning on air pollution. Asked no less than seven times whether the UK would maintain EU air quality laws following Britain's withdrawal from the European Union, Ministers both refused to make such a commitment.
Air pollution is responsible for at least 50,000 preventable deaths in the UK every year. It bears repeating that these deaths are entirely preventable. Poor air quality is also linked to respiratory difficulties, heart disease, and even, most recently, Alzheimer's; conditions that can seriously blight people's quality of life. Everyone is at risk, but children are particularly vulnerable, and if their developing lungs are affected the damage is permanent and life-limiting.
It is a public health emergency estimated to cost the UK £20bn a year. But it is not a uniquely British problem. In fact, air pollution has no respect for national borders. Air enjoys the freedom of movement regardless of Britain's status within, or outside of, the EU. The measures taken to control toxic pollutants in France and Spain directly affect the quality of the air we breathe in Britain, and vice-versa. Air pollution is a truly cross-border issue. One which requires truly cross-border solutions.
In fact, the British government has openly admitted that its efforts to improve the quality of the air that we breathe have been entirely driven by cross-border EU laws. Laws which have been carefully drafted in cooperation and collaboration with our closest European neighbours. The totemic legislation is the 2008 clean air directive.
The directive set legally-binding limits on toxic air pollution in towns and cities across Britain. However, the European Union's influence on UK air quality dates back to the 1970s, with the clean air directive just the latest in a series of air quality laws that have helped tackle air pollution in Britain.
The image of Britain as a 'dirty man of Europe', cast out by the continent, might seem farcical to those lucky enough to be too young to remember the 1970s when the UK was causing 'acid rain' that was destroying Scandinavian forests and lakes. But, for those of us with memories of a little more vintage, it is a useful reminder of just how far we have come by working together with our neighbours. Current European air quality laws are responsible for helping prevent 80,000 deaths a year across Europe.
Together we can and must do more. Environment ministers from across the European Union are currently discussing proposals for a new National Emission Ceilings Directive that will reduce air pollution at its source. The proposed law would set strict emissions limits for four deadly air pollutants, including nitrogen oxides, non-methane volatile organic compounds, sulphur dioxide, and ammonia.
At the same time, in the UK, the Conservative government is consistently turning a blind eye to the air pollution crisis, despite its promises to be the 'greenest government ever'. In fact, the government has already been successfully challenged in the Supreme Court by environmental lawyers, and vocal air quality champions, ClientEarth, over its failure to take action to ensure that British towns and cities don't breach the air pollution limits enshrined in EU law.
Earlier this year, ClientEarth were again granted permission to haul the government before the courts to challenge its repeated failure to publish plans to meet the limits, as required by the initial legal challenge. Dozens of UK cities are not forecast to meet the limits until a long time after 2020. Assuming, in that time, that air pollution in the UK doesn't worsen the government is prepared to turn a blind eye to another 200,000 avoidable deaths.
More than that, UK ministers have also been the most fervent lobbyists against tightening EU air pollution limits. The UK government is refusing to take the action necessary to prevent the avoidable deaths of hundreds of thousands of Britons.
Perhaps most telling, however, is that one of the men tasked with negotiating the UK's exit from the EU, Boris Johnson, has been accused of holding back a critical air pollution report during his time as London Mayor. The report, now leaked, reveals that it is the poorest and most vulnerable in our towns and cities that are exposed to the highest levels of deadly air pollution.
Johnson was also famously accused by the Clean Air in London campaign in 2012 of 'public health fraud on an industrial scale' for spraying dust suppressants in front of air quality monitors along the Olympic Route Network.
Therefore, when concerned members of the public asked me, during the referendum campaign: "Why wouldn't we just uphold the laws we have now, even if we leave the European Union?' I couldn't answer with certainty, but had to trust the evidence available and explain to undecided voters that it was my sincere belief that the air we all breathe would become more noxious should we vote to end our collaborative relationship with the European Union.
Unfortunately, for the health and prosperity of British citizens, Therese Coffey and Robin Walker, under scrutiny in parliament, appear to have confirmed my worst fears. It was a truly concerning response from Ministers.
In a separate development, the government has responded this week to the Commons Environment, Food and Rural Affairs report on air quality in the UK. And, to add to the uncertainty surrounding the UK's air quality policies, in its response, the government has decided to praise the very EU pollution limits it is failing - and outright refusing - to meet, has fervently lobbied against, and to which it is now refusing to commit. It remains the case that the only thing certain about Brexit is uncertainty.
"People will die," was the cautionary and frank response offered by ClientEarth chief executive of James Thornton when asked what would happen if Britain failed to retain the air quality laws it helped create. For improving the quality of the air we all breathe, the importance of European Union air quality laws cannot be overstated.
Leaving the EU must not be allowed to become a cover under which the government abdicates its responsibility for this public health emergency. Ministers must be bold and clear and make a firm commitment to maintaining and strengthening vital EU air quality standards.