ICM phone poll: Remain 48 / Leave 52

There has been a 14-point swing in favour of Leave since ICM's last phone poll in mid-May

The majority of phone polls published recently had indicated comfortable leads for Remain

ICM's latest EU referendum phone poll conducted for The Guardian newspaper shows that there was an incredible 14-point swing in favour of Britain leaving the 28-nation bloc since the research firm last surveyed public opinion earlier this month.

This means that the Leave campaign has gone from trailing Remain by 10 points in mid-May (45 / 55%) to enjoying a four-point lead at the end of the month (52 / 48%).

This is a very significant development for two major reasons.

Firstly, because such a huge swing in public opinion over such a short space of time is unprecedented.

Secondly, because up until this week, the results of pretty much every opinion poll conducted over the phone showed leads for Remain ranging from steady to very commanding.

In fact, it was only polls conducted online that were giving any sort of hope to those campaigning for a Brexit over the last few weeks.

However, ORB's most recent phone poll published yesterday gave Leave a cause for quiet optimism as it showed that Remain's margin of victory had been slashed from 13 points down to just 5.

That's why ICM's latest phone survey isn't just another poll — it's a sign that a seismic shift in public opinion may well be taking place with just over three weeks to go until the June 23 referendum.

Prime Minister speaks to the public alongside London mayor Sadiq Khan about why Britain should remain in the EU. Yui Mok / PA Wire /Press Association Images

Interestingly, the results of ICM's latest phone poll produced exactly the same final outcome as the online version.

Once the undecided respondents were excluded (9%), 52% of people surveyed online said they planned to vote for a Brexit, while 48% said they will vote to stay next month.

ICM's latest release will concern Remain campaigners. The tendency of phone polls to give a leads to Remain had seemingly become the only real predictable element of EU referendum polls.

Now that the trend is broken and public opinion appears to be moving in favour of a Brexit, it looks like the outcome could be a lot closer than everyone thought at the beginning of the month.