President Obama answers questions from an audience in central London on April 23. (Justin Tallis/Agence France-Presse via Getty Images)

Chris Grayling is leader of the British House of Commons.

Imagine if you were told that the United States should join an American Union bringing together all the nations of North and South America. It would have its own parliament — maybe in Panama City, a place on the cusp of the two halves of the Americas. That American Parliament would have the power to make the majority of your laws. A Supreme Court of the Americas in Panama would outrank the U.S. Supreme Court and take decisions that would be mandatory in the United States.

An Army of the Americas might do away with antiquated ideas such as the United States having its own military.

And to achieve this dream, every citizen of the Americas would have the right to live and work wherever he or she chose across the whole of North and South America. Why shouldn’t every Mexican have the freedom to move to New York City?

That is, more or less, where Britain finds itself today. We are part of such an organization. The European Union began as an economic partnership, designed to facilitate cross-border trade — in many ways just like the North American Free Trade Agreement.

But it has become something very different. It has its own parliament and supreme court. It makes around 60 percent of our laws. It decides the working conditions in our factories and offices, the rules that govern our housing estates and transport system, how our farmers work their land, how we drill for oil, how we research cancer, how we protect our consumers, the hours our doctors work.

It decrees that any citizen of any European country can come and live and work in Britain — and that if they do, we must give them free health care and welfare support if they need it. Millions have done so.

It’s not yet quite a United States of Europe, and we still have our own military. But it is moving closer and closer to becoming a single government for Europe, and indeed many of its key players — leaders such as Germany’s Angela Merkel and France’s François Hollande — have that as a clear goal. Britain has a small minority of the voting rights, and loses out almost every time.

The United States and the European Union may be comparable in terms of size, but they are very different. It is much more accurate to consider the differences between parts of the European Union in terms of a comparison between the United States and Bolivia, rather than one between Nevada and Maryland. Different countries, different cultures, different economies, with huge gulfs between them.

The United States would never accept a situation in which the countries of Latin America could join together and decide what laws should apply in Washington. It rightly expects to be a strong, independent country. That’s what I want for Britain, too.

But where does that leave the United States, and our mutual friendship?

When President Obama visited London in April, he made it very clear that he believes Britain should stay in the E.U. As our June 23 referendum on the question approaches, a number of other U.S. politicians have made similar arguments. Often they have done so with honest intent and with what they believe to be the best interests of Britain at heart.

But the view from Washington isn’t the best way of judging what is right and wrong for Britain. In the same way that Britain should respect the big decisions taken in the United States, the verdict on the future of Britain must be rendered by the people of Britain alone.

Inside or outside the E.U., Britain’s relationship with the United States will and must remain strong. Neither of us should ever be at the back of the line when it comes to working together. If Britain chooses to leave, our partnerships in defense, intelligence, counterterrorism, trade and culture should remain strong. Neither of us would benefit from growing apart, and neither of us should want that to happen, regardless of how Britain chooses to shape its future.

We have a unique and special relationship that has survived changes of government and changes of circumstance. That relationship will and must stay strong regardless of how the British vote in June.

And our friends here in Washington and across the United States should understand the challenge we face — and should stand aside as we reach our own best view about how we secure our future.