Professor John Curtice calculates a weighted average of all published polls, and says that the new data from ICM is very much in line with what he is seeing elsewhere. Whereas Remain had been running at around 54% overall in his series at the start of the year, this has now dropped to 51%, a figure that means “this referendum is now an awful lot closer than it was meant to be”.

The tightening, Curtice explains, is entirely explained by movement in telephone surveys. “Whereas internet polls have for months been suggesting a country that is split down the middle, until recently this was offset by the surveys done over the phone, which were recording a far higher share for Remain, sometimes approaching 60%”. But with the last few telephone polls, this proportion has dipped below 55%, a trend confirmed in today’s Guardian survey.

Curtice suspects that the true strength of anti-European sentiment is most likely to lie somewhere between the phone and the internet scores, recalling that at the general election online surveys tended to overstate Ukip, whereas telephone polls understated them. Martin Boon, director of ICM Unlimited, agrees, cautioning Remain campaigners against complacently assuming that the telephone polls must be right. “The majority of Labour voters are for Remain, and there are simply too many of them in telephone samples. Today’s monthly phone poll is the eighth since the general election where the sample recalls voting in Ed Miliband as prime minister last May.”

Both of today’s ICM polls used the same question wording, and deploy similar adjustments and weighting schemes. For general election voting intention, the telephone poll puts the Conservatives on 38%, Labour on 33%, Ukip on 13%, the Lib Dems on 7%, the Scottish Nationalists on 5%, the Greens on 3% and Plaid Cymru on 1%.

Today’s five-point lead for the Tories comes after a difficult couple of month for the government since the Budget, and contrasts with some other recent polls which actually put Labour ahead.