It has also emerged there has been a surge in inquiries about postal voting, which could produce a record number in the autumn poll. In the 2012 local elections in Scotland, postal votes accounted for one in four ballots cast. It is estimated that there are some 800,000 Scots south of the border, mostly in England with around 100,000 in London.
Under voting rules, a person over 16 is eligible to vote in the independence referendum if he or she is resident in Scotland and has their "substantive" home here, so they spend most of their time living there.
A spokeswoman for the Electoral Commission, the elections watchdog, said while no problem had yet been detected with expatriate Scots seeking to register so they can have a say on Scotland's future, electoral registration officers have been placed on their guard and were "very alert" to any intended abuse of the system.
She explained that under the 1983 Representation of the People Act, those committing a voting offence could be jailed for up to a year and/or fined a maximum of £5000.
Asked about security and abuse of the system from Scots living south of the Border, the spokeswoman said: "The electoral registration officers are very alert to that. They know their local properties inside and out and will spot if there are too many applications. If someone says a property is their substantive home and it isn't, they are breaking the law."
She added: "There isn't a problem as yet but the electoral registration officers would talk to the police if there was."
At the last count, two years ago, there were just in excess of four million eligible voters in Scotland.
By law, an eligible voter can register to vote for the September 18 referendum as late as 12 working days before the ballot, ie September 3.
If someone wants to vote by post, or chooses a proxy to vote on their behalf, they also have until September 3 to apply. The postal and proxy votes will be effective right up to the close of the polling stations at 10pm on September 18.
In 2003, just 4% of votes applied for were postal. By 2012, the proportion had almost quadrupled to 15%. But that 15% represented 26% of the actual votes cast. Indeed, statistics show that a person using a postal ballot is twice as likely to cast it as someone doing so in person.
Two years ago in the Scottish local elections, the turn-out among those casting their votes in person was 35% while that for postal voters was 70%.
The spokeswoman revealed that just after Christmas there was a surge in public inquiries about postal voting for the referendum; put down, in part, to people trying to work out their potential whereabouts around their summer holidays.
If there were an increase in postal votes for the referendum, Scotland's future could be decided from the armchair.
While it is thought the vast majority of the 800,000 Scots living south of the Border will be ineligible to vote in the referendum, by contrast most of the 400,000 English, Welsh and Northern Irish citizens with their main homes north of the Border will be eligible.