Labour’s problem in the EU election was simple but fundamental. It had overwhelmingly remain members but a Brexit message. It was a remain party whose leader played both sides so unconvincingly that, as Lloyd George said of Sir John Simon, the architect of appeasement: “He has sat on the fence so long, the iron has entered his soul.”

For the sake of the country and the party, we now have to be clear about our opposition to Brexit. For me personally, the election was excruciating. Resistance to Brexit is the logic of everything Labour stands for. Yet instead of an unambiguous statement of support for a referendum with an option to stay in the EU, we fought on a formula akin to the design manual for a submarine – and one never intended to come to the surface. Labour party members, as well as supporters, were angry and bemused.

Brexit is not a viable path for Britain. It was probably never viable, but it has long since become clear that a wholesale renegotiation on the basis of Labour’s six tests for any deal, seeking to maintain the benefits of the single market and the customs union, is practically impossible. In the European elections, the Lib Dems and the Greens outpolled the Brexit party, and if you add up the pro-remain votes, there is every indication that a substantial majority of the public now oppose Brexit.

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Opposition to Brexit has turned to alarm as Nigel Farage completes his takeover of the Tory party and converts it to the pursuit of no deal – a crazy, ludicrous policy that was never proposed, even by Farage, before the 2016 referendum.

Labour is the party of the NHS and the environment and fighting for better workplace and civic rights for working men and women. From the ruins of the second world war, Labour rebuilt Britain and set it on course for European co-operation and membership of the EU. European unity and social democracy have advanced hand in hand as surely as the EU, together with Nato, have secured the peace of a continent long ravaged by bloody conflicts. The EU is our mission, not a flag of convenience.

We cannot continue with a cocktail of confusion. We owe it the country to be honest, and to lead strongly against Farage.

Last year’s Labour’s conference supported the option of a second referendum if we failed to get a “good” Brexit or a general election. The time has come to make a second referendum our clear and settled policy, and for Labour to declare that it will lead the remain campaign.

With the Brexit party rampant and a Faragist Tory leader imminent, we do not have the luxury of time to secure this mandate at Labour’s autumn conference, four months away. The party should, without delay, hold a referendum of party members to decide for, or against, support for a second Brexit referendum and Labour’s policy in that referendum.

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Principle not ambiguity; clarity not dishonesty; leadership not fence-sitting. These are the foundations for Labour’s future success as a party of principle and of government. They are what the country desperately needs, and we have a duty to provide.

As for Simon, he tried to come off the appeasement fence when Churchill became prime minister. But the great Nye Bevan demolished him with one line: “No one believed that he believed.”

• Andrew Adonis is a Labour peer, and former transport minister. He stood to become a Labour MEP at the European elections