Over 4 million people are set to cast their vote in the Scottish independence referendum on Thursday (18 September), with a record turnout expected as 97 percent of eligible voters have registered for the poll.

Polling stations open at 7am local time and close at 10pm. Exit polls are expected immediately afterwards, while the final result should be known early Friday morning.

Opinion polls published in the last few days suggested the result will be too close to call, with the No camp ahead by two-three percent, which is within the margin of error.

If Scotland votes Yes, it will represent a political shock for the EU.

Spanish prime minister Mariano Rajoy on Wednesday called it a “torpedo below the waterline for European integration”. He warned that an independent Scotland would have to re-apply for EU membership and that the process will take years.

Spanish foreign minister Jose Manuel García-Margallo said that “it would start a process of Balkanisation that nobody in Europe wants,” a reference to smaller states breaking off and becoming hostile to each other.

Madrid has weighed into the Scottish debate because it opposes a similar referendum from taking place in Catalonia. Local authorities want to hold a non-binding “popular consultation” in November.