But he has had little or no impact on the debate in Parliament.

He does seem to still have influence with President Trump, for whom he campaigned, and who recently dismissed Mrs. May’s deal in terms strikingly similar to those Mr. Farage had just used on Fox News.

Yet Mr. Farage never managed to win a seat in the British Parliament, let alone secure a ministerial post. He no longer has a political party, as he resigned from the U.K. Independence Party that he had led more than once, accusing its current leadership of tolerating right-wing extremism.

And although he is still a member of the European Parliament, he will lose that position next year when Britain leaves the European Union, thanks to the Brexit he has championed for more than two decades.

If there is a living, breathing example in politics of the saying “Sometimes when you win, you really lose,” it is arguably Mr. Farage. So how does it feel to be in his shoes at the moment?

Usually his replies come in rapid fire, but this time he pauses.

“Frustrating at one particular level,” he eventually answers. “There are some people who think this dog’s dinner of a deal is my fault, because I pushed for Brexit. To which I robustly respond by saying this is not the Brexit, or anything like the one I would have gone for.”