There is one important thing you have probably forgotten about the EU referendum

David Ramos / Stringer

Brits who have lived abroad for less than 15 years are able to vote by post.

The race to decide the United Kingdom's future is growing increasingly tense, with just three days to go until the EU referendum.

However, there is one key detail that people often forget - lots of people have already cast their votes.

The opinion polls have been very volatile this month with public support seemingly swaying from one campaign to the other. Many Brits are yet to fully make up their mind, or are open to persuasion.

But a significant number of people have already come to their own conclusions, and have submitted their votes by post.

Around 16.5% of those who participated in the 2015 General Election used the postal voting system, and just over 20% of Scottish independence referendum voters did the same, according to Electoral Commission data. These were big enough shares to be statistically important.

And it's highly possible that the share of people who will vote in the EU referendum by post will be even larger, given that June 23 clashes with the hugely popular Glastonbury festival - and also falls at a time of year when people are more likely to take holidays.

This often-forgotten fact highlights just how much importance rested on the Leave and Remain campaigns putting forward compelling cases throughout the race - not just in the week before voting day when most undecided people will pick a side.

It also means that moments in the race like TV debates and the publication of the UK migration report could have been even more significant than people initially thought, as people who voted by post may well have come to a decision based on this events.

The number of British people who will be casting their votes (by post) from abroad must be considered. A change to the UK's relationship with the 28-nation bloc would likely have an impact on the privileges they are entitled to in their host nations, meaning they have a clear interest in taking part.

According to the latest opinion polls, the Remain campaign has fought back after a week of Leave momentum to lead in polls conducted by ORB and NatCen.