The idea of European citizenship has its roots in the aftermath of the second world war, when Winston Churchill spoke of a “common citizenship” that would unite Europe together “in the sharing of its common inheritance”.

Why I helped bring the Dutch case over Britons’ EU rights | Jolyon Maugham Read more

This concept of a union of people – not merely of nations – was recognised by the European court of justice (ECJ) shortly after the formation of the European Economic Community (with the treaty of Rome) in 1957. But it was in 1993 that our cultural identity as citizens of Europe first took legal form. Today, article 20 of the treaty on the functioning of the EU states that “citizenship of the union shall be additional to and not replace national citizenship”.

European citizenship confers a number of privileges: the right to live in and move freely between member states, the right to diplomatic and consular assistance from other member states, and the right to participate in elections to the European parliament.

The shared assumption of the European Union and the UK government is that Brexit will mean British citizens will automatically forfeit these rights. But this is being tested in a case brought by a group of UK nationals living in Amsterdam, which I funded with the help of Dutch law firm Bureau Brandeis, which agreed to act for a modest fee.

I am a Londoner, I am British, and I am European. They’re not mutually exclusive

Earlier this month the judge, Floris Bakels – a former vice-president of the Netherlands supreme court – said after hearing the argument from both sides that “there is reason to doubt the correctness of the interpretation of article 20 that the loss of the status of citizen of an EU member state leads to loss of EU citizenship as well”. He decided to refer it to the ECJ: the only court that can decide whether Brexit must entail a loss of EU citizenship.

In my view, this is one of the most important questions to come before the courts in modern times. If our case is successful it will make legal history.

But the Netherlands has sought to appeal the decision to refer the question to the ECJ. I am crowdfunding to cover the legal costs of defending that appeal in the Dutch courts.

We don’t know which way the ECJ would rule if the case went to it. But the ECJ has been bold on these issues in the past.

Our EU citizenship does not replace our national citizenship. But like our national citizenship, it is an important part of our cultural history and our legal identity. I am a Londoner, I am British, and I am European. They’re not mutually exclusive. And our rights to European citizenship – and all the privileges that confers – are worth fighting for.

• Jolyon Maugham QC is a barrister and director of the Good Law Project