If David Cameron loses the referendum, he'll go down in history as a failure

The Prime Minister needs Jeremy Corbyn to persuade Labour supporters to vote to stay in the EU, and the Labour leader made a good attempt on Thursday, but it may not be enough

One moment David Cameron was the hero winner of an unwinnable election, the next he was staring at the all-too-likelihood of being a former prime minister with no obvious achievements to his name, who didn’t even last as long as John Major, the comma in recent British history.

Cameron deserved more credit than he was given for winning last year’s election. It wasn’t possible, they said, for a governing party to increase its share of the vote. The opinion polls said so too. He showed steel, focus, self-belief and a deep understanding of the British people. He earned the right to impose his vision on the country and, at last year’s Conservative party conference, he set out a programme that seemed to answer the moment: an all-out assault on poverty, on mental illness and on a prison system that only turns soft criminals into hardened ones.

Six months later and triumph is about to be swallowed by disaster. I won’t predict the result of the EU referendum – we sayers of sooth have learned our lesson over the past year – but I think a vote to leave the EU is more likely than people think. Certainly, the Prime Minister is worried. He fears that Labour voters are not much motivated to turn out on 23 June.

That was why Jeremy Corbyn’s speech on Thursday was so important. I thought he made a clever and effective speech. He softened his opposition to the Transatlantic Trade and Investment Partnership (TTIP), the free-trade deal being negotiated between the EU and the US. Which is just as well, because, even if you think TTIP is an oppressive capitalist conspiracy, which it isn’t, no EU member state has to accept it, so it isn't much of an argument against EU membership.

Instead, Corbyn praised the virtues of the EU as protector of workers’ rights and a bulwark against the worst excesses of Tory rule. He delivered a cynically partisan warning that, if we left the EU, “it wouldn’t be a Labour government negotiating a better settlement for working people with the EU – it would be a Tory government, quite possibly led by Boris Johnson and backed by Nigel Farage”. Farage has nothing to do with it, but he is more alarming to Labour activists than Johnson.

As a political obsessive, I enjoyed the skill with which a lifelong Eurosceptic managed to make the opposite case in a way most likely to appeal to his own side. But as an obsessive, I am liable to exaggerate how much Corbyn’s anti-EU past has confused Labour’s referendum message. Among those who think they know, voters divide about four to one in believing both Corbyn and the Labour Party to be on the side of “Remain” rather than “Leave”. The problem is that 40 per cent say they don’t know. One of the aims of the Remain campaign over the next two months is to inform them that Labour supports staying in the EU.

When it comes to it, though, the Prime Minister is still relying on Labour supporters to come out to vote for the option he, a Tory retoxified by the Panama Papers, advocates. Which might work if the arguments for staying in the EU were as compelling as he thought they were.

I was struck by a poll carried out last month by James Morris of GQRR for the Fabian Society. Olivia Bailey of the Fabians reported: “After voters are exposed to detailed arguments on both sides of the debate, the race shifts in Leave’s favour.” By asking how people intended to vote at the start and the end of the survey, it found a two-and-a-half-point swing to Leave after respondents were shown the main arguments from both campaigns.

Never mind the headline figures suggesting a close result – those are not worth much at this stage – that is the kind of finding to get Cameron thinking of getting Samantha and the children into the gallery of the House of Commons to witness what might be his last Prime Minister’s Questions on 20 July.

He had been banking on the “fundamentals” of the economy to win through this time, as they did in the Scottish referendum and in the general election. But those fundamentals may not be the same this time, as he is posing abstractions such as GDP and inward investment against people's personal experience of the free movement of EU workers.

Why, he must be asking himself, did he promise the referendum in the first place? But he knows the answer to that better than most: because he couldn’t have won the 2015 election unless he had done so. It bought him unity in his own party, and stemmed the loss of votes to Ukip (which ended up taking nearly as many votes from Labour as from the Tories), just enough to get him across the line.

So that could be the end of him, in just 10 weeks’ time. If he loses the referendum, he would "not last 30 seconds" as Prime Minister as the pro-EU Kenneth Clarke put it on Friday, let alone the two years it might take to negotiate Britain’s separation from the EU. His party wouldn't have him. There would be no time to start his all-out assault on poverty, let alone to finish it; and he would have served six years and one month as Prime Minister against Major's six and a half years.

He would be cut down in his prime, not yet 50, with a caretaker record as the Prime Minister who managed to close only 63 per cent of the post-crash deficit; who fought a war in Libya that made things worse, like Iraq but smaller; and who kept Scotland in the UK only to see it gearing up for a second referendum, this time to break away to rejoin the EU.

The cruelty and caprice of politics is quite something.