England fan wears mask of Queen Elizabeth II in Saint Etienne - EURO 2016 Reuters/Wolfgang Rattay The referendum on whether the UK should "Remain" or "Leave" the European Union is currently one of the most difficult electoral events to call in British history.

However, analysts at HSBC have flagged up 10 places in Britain that could potentially indicate the outcome of the referendum when they publish their results.

Polls in the lead up to the referendum have swung wildly between the Leave and Remain camps, and no one is entirely sure which way the vote will go.

To make things even more difficult to predict, when polls close at 10.00 p.m. BST (5.00 p.m. ET) on the day, there will be no official exit poll.

Unlike in a general election — when the exit poll usually provides a pretty clear idea of the result — Brits and those watching will have to wait for actual results to start coming in. The first results are expected to be within two hours of polls closing, with Sunderland in the northeast likely to be the first to declare.

To provide something of a bellwether of how voting may go, HSBC's chief UK economist Simon Wells and his team have provided a useful table showing some of the key areas that could help determine whether Britain stays in or leaves the EU. The areas listed are those where public opinion has generally been close to the UK average, meaning that the way these places vote could be a strong indicator of the way the country as a whole goes.

Take a look at HSBC's chart below:

And here is what Williams had to say:

Interpreting the results as they come in will be difficult, given the lack of precedent. Unlike in a general election, no-one knows the key 'swing areas'. This is one reason why there will be no authoritative exit polls. However, past surveys of public opinion on the EU can identify regions that might give an indication of the national mood. While these surveys were not intended to poll voting intentions in the upcoming referendum, we can use them to highlight areas that are closest to the national average when asked about attitudes to the EU.

Another crucial area for the referendum will be the northwest city of Lancaster, which could give us a massive clue about the final result hours before the official declaration. According to Chris Hanretty, Reader in Politics at the University of East Anglia. In a recent blog post, Hanretty explains that public opinion towards Britain's EU membership in Lancaster is very close to the national median.

Polls ahead of the vote are mixed.

Late last week it looked like the Leave camp was taking a solid lead, but since the tragic murder of MP Jo Cox, polls have shown a swing back towards Britain staying in the EU. The most recent poll for the Daily Telegraph showed a solid lead for the 'In' camp. Remain leads Leave by 53% to 46%, with 2% saying they don't know. The poll was carried out by ORB International and had a survey size of 800 people.