I HAVE been thinking about the old Jewish joke about the man rescued after years on a desert island. Before he leaves, he gives his rescuers a tour of his domain. “This is my house,” he says. “And this is my synagogue.” “And what,” the newcomers ask, “is that over there?” “Oh,” he replies, “that’s the synagogue I don’t go to.”

Once, politics was like that. I have been wondering how to vote in the European elections next week. For most of my life, the salients of the political landscape were clear. This was the party that I voted for, and that was the party that I did not vote for. Dotted around were a few other parties, which I considered when someone I knew was standing.

Brexit has changed everything. The political compass no longer points Left or Right, but Leave or Remain. The fact that these are European elections intensifies that. Local elections can be a proxy for national issues; but this is overtly an election about what should be our national relationship to our cousins on the Continent.

If you are a Leaver, you have a clear choice. The party making the running in the polls — outnumbering Conservatives and Labour put together — unadornedly calls itself the Brexit Party. And there is the variation of UKIP, for those who just cannot stand Nigel Farage, the leader of the Brexit Party.

Both the main parties have lost it. The Tories are the custodians of Chaotic Brexit. Labour’s supposed counter-offer is merely Confused Brexit. Voters are quitting both in droves, the polls suggest, unless they are Soft or Reluctant Brexiters.

But how do you vote if you favour Remain? You can choose Liberal Democrats, Greens, Change UK — the Independent Group, SNP, or Plaid Cymru. But you get to make only a single cross on the ballot in European elections here. The way the poll is counted is proportional, but you do not get a transferable vote, as voters in Northern Ireland do in the same elections. That means that the Remain vote is almost certain to be disastrously split — to the advantage of Brexit bombasts.

Gina Miller, the businesswoman who went to court to ensure that Parliament had the right to vote on Brexit, has come up with a strategy to combat that. She has set up a website, remainunited.org, on which voters can register to be given advice, just before the vote, on the basis of an analysis of the latest polls, on how they should vote tactically in their particular constituency to maximise the Remain vote.

Tactical voting is a tricky business at the best of times in the UK. But it is even more complex with these European constituencies, and their closed d’Hondt lists (you will have to look it up, I’m afraid). Some Labour supporters are still sore with the LibDems after voting for them to keep the Tories out in 2010, only to find them entering into a coalition with them.

Perhaps we will just have to stick with the old-fashioned notion of voting according to principle. I’ve never voted Green, because their economic policies seemed unrealistic. But with the accelerating rate of global warming, perhaps the time has come to think of that.