Sir Vince Cable, the leader of the Liberal Democrats, is entirely justified in criticising other parties that share his desire to keep Britain in the European Union. As we report today, the Lib Dems claim to have proposed to Change UK – the party formed by the Independent Group of MPs – and the Green Party that they should unite to fight the European parliament elections together.

“We didn’t get a positive reaction to that, so we are going on our own,” Sir Vince told the BBC. He should not give up so easily.

The position taken by Change UK and the Green Party appears to be based on a misunderstanding of the voting system used in European elections in Great Britain. One Change UK MP confidently explained to a journalist that “the beauty of the system meant it was impossible to split the Remain vote”, while the Green Party explained on Twitter why it had no plans to field joint pro-EU lists, saying it was “a proportional election, meaning every vote has equal weight – tactical lists are not necessary”.

Farage launches his new Brexit Party: in pictures Show all 10 1 /10 Farage launches his new Brexit Party: in pictures Farage launches his new Brexit Party: in pictures Nigel Farage speaks at the launch of his new Brexit Party's campaign for the European elections Reuters Farage launches his new Brexit Party: in pictures Brexit Party candidate Annunziata Rees-Mogg, sister of Conservative MP Jacob Rees-Mogg, speaks at the launch AFP/Getty Farage launches his new Brexit Party: in pictures A supporter waits for Farage to speak AFP/Getty Farage launches his new Brexit Party: in pictures Supporters wait for Farage to speak AFP/Getty Farage launches his new Brexit Party: in pictures Farage's socks Reuters Farage launches his new Brexit Party: in pictures Farage and prospective candidate Annunziata Rees-Mogg wait at the launch AFP/Getty Farage launches his new Brexit Party: in pictures Supporters listen as Farage speaks AFP/Getty Farage launches his new Brexit Party: in pictures Free T-shirts for all attendees AFP/Getty Farage launches his new Brexit Party: in pictures Posters on the seats for supporters of the Brexit Party AFP/Getty Farage launches his new Brexit Party: in pictures A safety sign is pictured AFP/Getty

Unfortunately, the form of proportional representation used in these elections is one of the worst ever devised. It is almost as if it were designed to give electoral reform a bad name. Voters are required to choose between party lists with a single cross. The parties themselves decide the order in which their candidates are ranked, with the top candidate elected first – there is a row raging in the Labour Party at the moment over the order of its London region list.

Because voters are unable to rank either parties or candidates in order of preference, parties standing on similar platforms are liable to lose out by splitting their vote. The Lib Dems, Greens, Change UK, the Scottish National Party and Plaid Cymru all support our membership of the EU and want to put the Brexit decision back to the people in a Final Say referendum.

None of them on its own currently stands higher than 10 per cent (the Greens) in a Great Britain opinion poll, whereas together they account for 29 per cent. Only in one region does 10 per cent guarantee a party a seat in the European parliament. That is in South East England (excluding London), a region with 10 MEPs. In North East England, for example, which has three MEPs, a party needs 25 per cent of the vote to guarantee winning a seat.

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It is bad enough that the Labour Party continues to equivocate about a new referendum, but the refusal of the parties with a clear position to work together is self-defeating.

The European elections are an important opportunity for both sides of the Brexit argument. Indeed, if, as seems quite possible, the UK stays in the EU for the foreseeable future, the country ought to be represented in the parliament by MEPs who want to make the EU work for all its citizens.

Instead, so far, the Brexit Party led by Nigel Farage is making the running, with a clear message and a good chance of squeezing the vote of his former vehicle, Ukip. The new party has already taken the lead in a poll published today.

It is not too late for the Remain parties to cooperate. It may not be possible for them to present joint lists at this stage, but there is still time for the parties to stand aside in favour of each other in different electoral regions.

Nominations for candidates close on 25 April (24 April in the South West region, because Gibraltar, which has different public holidays, is part of it), and any nominations may be withdrawn by then.