Opinion polls misled us all in 2015, but now they're as powerful as ever

Opinion polls determined the course of UK politics in 2015. They will do so again this year, even though some politicians and journalists had resolved to view them with greater scepticism. In the build up to the general election, polls triggered endless speculation about what would happen in a hung parliament. There was no hung parliament.

For reasons that tell us much about the febrile state of politics the pollsters’ election trauma is already a distant memory for those who declared they would pay them less attention. The polls will decide precisely when David Cameron calls a referendum on the UK’s membership of the EU, the most important decision of his leadership. In the other great saga of British politics they will also be the key factor in the fate of Jeremy Corbyn. An unpopular leader, even if adored by his or her party, is vulnerable. A popular one acquires authority and a freedom to act. More than ever we live in the era of the opinion poll.

Assuming Cameron completes his negotiation at the EU summit next month, he hopes to hold the referendum in June. But he would be reckless to announce it immediately after the summit. Before naming the day he will consult the polls. If they suggest voters are giving his renegotiation the thumbs down he will not call a referendum.

Leaders do not consult voters when it looks as if they are going to lose, especially when there is flexibility about timing. Cameron has until 2017. After his renegotiation both sides will scrutinise polls feverishly – private polls, public polls, every bit of evidence as to which way the debate is going. It will be as if 2015 and the outbreak of opinion poll scepticism had never happened, and for good reason too.

If those who want to leave the EU appear to be moving well ahead, Cameron will have no choice but to make an excuse about more time being required. He will not admit he is delaying because he is worried about losing. No leader makes such an admission, that they twist and turn depending on the mighty opinion polls.

Cameron delivered his best joke when Gordon Brown called off plans to hold an early election in the autumn of 2007. Brown changed his mind at the last minute because polls showed a significant swing away from Labour in marginal seats. He pretended he was acting in the national interest and that his decision had nothing to do with the polls. Cameron responded by suggesting that Brown was the first Prime Minister not to call an election because he was afraid he was going to win.

Similarly, if Cameron decides not to go for a June referendum if the polls are against him he will insist it is in the national interest. On the surface he will be the first Prime Minister not to call a referendum because he is afraid he is going to win.

The Prime Minister will spend the second spring in succession worrying about opinion polls. Corbyn has probably been untroubled by polls for his entire political career. Whether he starts to study them neurotically like all his recent predecessors, or continues to view them with indifference, is largely irrelevant. The polls will determine what happens to him.

Corbyn’s internal dissenters know little about what they would do in policy terms if they were in charge. But they are united in their assumption that Corbyn is leading their party to calamitous defeat. While they make that assumption, Corbyn is vulnerable. He can change his Shadow Cabinet, give more power to party members and pull other levers available, but a leader of the opposition acquires invincible authority only if he or she looks like a winner.

If polls suggest Corbyn is a loser he will have less space to act in a way he would like and risks being removed. If polls suggest he is starting to appeal to the wider electorate, a lot of the dissenters would discover a loyalty to their leader. If Labour is miles behind in the polls there will be an attempt to remove Corbyn, possibly even this year.

There is a myth that Labour is sentimental about its leaders. Some cite the survival of Ed Miliband as evidence of this. But it was the mighty opinion polls that protected Miliband. There was not a single poll from his election as leader in 2010 until the exit poll last May that suggested Labour had no chance of forming the next government. Most showed that Labour would have the highest number of seats or an overall majority. Under such circumstances there was never any great momentum towards a coup against a leader who seemed on course to victory.

Arguably the polls saved Miliband as leader, all of them suggesting he had a good chance of becoming Prime Minister, and then wrecked his chances by legitimising the right-wing media focus on the apparent horrors of a Labour/SNP relationship in a hung parliament that never materialised.

When tribal loyalties are dying, no UK party is overwhelmingly popular, detached voters change their mind on issues suddenly and insecure leaders turn to referendums as a device to keep their parties together, opinion polls are their only reliable guide. Some Labour figures might have doubts about what it means to be on the centre-left but they want to win. As an alternative to clear ideas they turn to polls for vindication.

Cameron did not want to hold a referendum on Europe, but offered one to keep his party together and deal with an apparent threat from Ukip. Now he relies on polls as he decides when to hold the vote that will make or break his leadership.

The media reports on polls as obsessively as ever – for the good reason that they do have a big impact on insecure parties and leaders. They remain significant. The pollsters have little cause for misery about what happened in 2015. They are more powerful than they have ever been as nervy leaders and parties make their moves at the start of another stormy year.