Now we know that Brexit means Brexit, even if parliament votes against the deal negotiated by the Prime Minister.
The stark truth which has emerged over the last 24 hours highlights clear evidence that we should all be worried about the future of the UK's parliamentary sovereignty, which many are so keen to wrestle back from Brussels. And that matters hugely for the future of the UK's environment.
Yesterday Theresa May set out her thinking on leaving the EU. Yet while it came as welcome news that MPs and peers would be given a vote on the Brexit deal, today the Brexit Secretary David Davis brushed parliamentary sovereignty aside by saying that even if parliament votes against the plan, we will still leave the European Union.
The prospect of the UK Government ignoring parliamentary votes on such a significant constitutional issue and carrying on regardless must surely heighten fears that laws to protect the natural environment might also be ignored after repatriation from Brussels.
If this is how the government treats parliamentary sovereignty, then what hopes can we have that environmental laws, like those on pollution which the government doesn't pay much heed of anyway, won't be treated similarly once we leave the EU?
The government's approach shows a scandalous disregard for parliament.
The UK is due, within weeks, to spark the formal process of leaving the European Union, beginning negotiations triggered by the planned Article 50 notice.
But it is at home that the future of environmental protections in the UK will be determined. And it is crucial, now more than ever, that Parliament plays a central role.
In parallel to negotiations with Europe, Mrs May has confirmed that the Great Repeal Bill will enable the UK's exit - most centrally from a constitutional and political perspective, by allowing the repeal of the European Communities Act 1972.
However, it is the technical function of the Bill to which Parliament and those who care about the environment, health, and climate change must look. It's there that the foundations of environmental law must be established. And it's where the promised return of parliamentary sovereignty will be put to the test.
The law is the law. Or is it?
Theresa May has promised that existing laws will be maintained upon exit, that the Great Repeal Bill is the mechanism to achieve this and that converting EU laws will create as much certainty the day after Brexit, as there was the day before.
There are many pieces of legislation worth saving. UK air quality laws are, in blunt terms, a mess. But they are complemented by comprehensive European laws, to which the UK is legally bound and committed. These laws protect us with health-based standards that ministers cannot escape. They mean the government has to clean up our dirty towns and cities, making them more pleasant places to live and reducing the terrible health impacts of pollution.
It was a similar story in the 1980s, when the EU's clean bathing water laws improved the UK's polluted beaches - against the will of the government and to the great benefit of those enjoying blue flag beaches.
At the moment, some of these vital laws are not on the statute books; some are only in secondary UK regulations and some are in EU directives. This must change.
Turning EU laws into UK laws is not the end of the story, but the beginning. The Great Repeal Bill will draw a line that will determine the future law-making sovereignty of Parliament after the UK leaves the EU.
False sense of security
Let's not be lulled into a false sense of security. The Great Repeal Bill must go further. The Great Repeal Bill must affirm the role of Parliament and ensure that environmental laws are truly that: laws.
We need laws, on the statute books, that can only be changed or repealed by a fully sovereign Parliament. It is after the UK leaves the EU that fundamental environmental protections could be most at risk of a deregulatory agenda pursued by a minority of interests. They certainly exist.
By all means, the UK should embark on a public debate and engage actively in public policy processes. Let us pursue an active agenda of good government with white papers, public participation and pre-parliamentary scrutiny of legislation. That agenda should include the government's '25 year plan for Nature' - which must leave the natural environment in a better condition for future generations than now; the forthcoming emissions reduction plan - which will prepare the UK to meet its carbon budgets in the 2020s; and the government's new air quality plan - mandated by the High Court in the ClientEarth case to tackle illegal pollution levels as soon as possible.
Ultimately, post-Brexit, the UK should make environmental laws that suit the UK and its unique natural and social environment. This may include a new environment act as proposed recently by the Commons Environmental Audit Committee, as well as legislation for sustainable agriculture and fisheries management.
But the starting point must be the sovereignty of Parliament as the rightful law-maker. That sovereignty must be recognised first by 'saving' laws: maintaining the foundations of environmental law on our statute books and ensuring that future alterations can only be made by Parliament.
That means with all the rigour of the passage of bills through three readings in each House and the accountability of the government to parliament. These core constitutional functions must be asserted and respected.
Of course, many other questions must be answered and resolved in the process. But let's first recognise the question at the heart of the Great Repeal Bill: who will decide what happens to our laws in future? Rightly that must be Parliament.
Karla Hill is programmes director at ClientEarth and a Greener UK coalition board member