More than three years ago, the UK voted to leave the European Union. Shortly afterwards, the then prime minister, Theresa May, said this meant that the UK would leave the EU's single market and customs union.
Current prime minister Boris Johnson has confirmed this position, and the consequences of these decisions are clear: they create barriers to trade between the EU and the UK that do not exist today.
After two years of painstaking talks, the EU and the UK reached an agreement on operational solutions for a whole range of areas where the UK's withdrawal creates uncertainty: first, how do we make sure that UK and EU citizens continue to enjoy their existing rights, with strong enforcement mechanisms and lifelong guarantees?
What happens to researchers or organisations in the UK that get EU funding? What should we do after Brexit with the extradition of criminals that began under EU law? How do we ensure that Cypriots living in the UK sovereign base areas continue to enjoy their rights under EU law?
It is nine months since the 27 EU governments reached an agreement with the UK on the terms of an orderly withdrawal and on the framework for our future relationships. So far, Westminster has failed to approve the agreed package.
Some British MPs voted against it because they do not want Brexit at all, others because they would prefer a no-deal outcome. Some MPs said "nay" because they want a much closer economic relationship with the EU, others because they want a more distant future relationship and less stringent conditions on fair competition between the EU and the UK - for instance, on environmental laws and labour rights.
As the EU's chief negotiator, I know very well how divided the UK still is on what future it wants with the EU.
That is why the Political Declaration points to a free-trade agreement as a baseline and leaves open the possibility of a closer relationship with the EU should the UK's red lines evolve. In all circumstances, however, the relationship will consist of an appropriate balance of rights and obligations.
In the midst of the ongoing political debate in Westminster, I think it is worthwhile to point out there remain many misrepresentations about the solution we have found to avoid a hard border on the island of Ireland.
The backstop is all about managing the unique risks that Brexit creates in Northern Ireland - a fact Mr Johnson recognises in his recent letter to President Donald Tusk.
It is not about changing the constitutional status of Northern Ireland. That is none of the EU's business, as it is the Good Friday Agreement - an agreement between the British and Irish governments and political parties in Northern Ireland - that settles how Northern Ireland should be governed.
The backstop fully respects the carefully negotiated balance found in that agreement between competing political views and different identities in Northern Ireland.
Its objective is simply to have an insurance policy in place that guarantees that the border between Ireland and Northern Ireland remains fully open, and that the status quo of cross-border exchanges on the island of Ireland is maintained.
At the UK's request, we agreed to have a UK-wide customs dimension to that backstop. On the EU side, we had intense discussions with EU member states on the need to guarantee the integrity of the EU's single market, while keeping that border fully open.
In this sense, the backstop is the maximum amount of flexibility that the EU can offer to a non-member state. Why? Because the backstop provides Northern Ireland with the economic benefits of the single market for goods, which the EU is exceptionally willing to offer due to the unique circumstances on the island of Ireland.
I believe that the people of Northern Ireland recognise and appreciate this offer more than Westminster does for now.
The new UK government has asked us to change what was agreed. The EU had already committed itself to working with the UK during the standstill transition period on alternative arrangements that achieve the same objectives of the backstop. We are ready to start this work immediately upon ratification of the Withdrawal Agreement, in parallel to finally creating clarity on our future relationship.
I am not optimistic about avoiding a no-deal scenario but we should all continue to work with determination. The EU is ready to explore all avenues that the UK government may present and that are compatible with the Withdrawal Agreement. Uncertainty has festered for far too long in the UK, in particular in Northern Ireland, as well as in Ireland and all other EU countries, for that matter.
Boris Johnson has said there will be no more extensions beyond the end of October. Therefore, the UK has now come to a moment of truth and it must decide if it leaves the EU with or without an agreement. If it chooses the latter, it means that there will be no transition period and no so-called "mini-deals" - as the EU will act only to protect its own interests.
In case of no deal, all the UK's financial and other obligations from its past EU membership will continue to exist, as well as obviously the international obligations it has to protect the Good Friday Agreement, in all its dimensions.
The EU cannot prevent the UK from choosing a no-deal scenario. I would fail to understand the logic of that choice though, as we would still need to solve the same problems after October 31. Many people in the UK understand that and I would be surprised if they succumb to the idea that the EU is to blame for a difficult political situation in the UK.
Michel Barnier is the European Commission's chief negotiator